Well speaking from experience... this suggestion will not do what you
think it will.
Now the reason that UE4 and U3D have (some degree) of Cross-Integration is in-part out of Necessity., but also in-part because of Microsoft (Game Studios).
You have to keep in mind that Microsoft more-or-less own Unity today., and they also have a long-standing partnership with Epic for the Unreal Engine that is heavily used by most of their 1st Party Studios.
I've been hearing rumours that this is changing given Epic's unwillingness to give up their partnership with NVIDIA … but eh, let's not get into Industry Politics right now.
In any case, as Unity is used by … well everyone as at the bare minimum a Rapid Prototype Middleware for testing concepts, ideas, mechanics, etc. before them committing to Developing such on an in-house proprietary engine (my own studio has our Sunset Engine) or taking a deep breath and cracking open the Unreal Engine 4 Source (oh boy is that "Fun" to modify / expand / extend)., obviously there needed to be a way to fairly rapidly transfer between the two Engines to switch between Prototypes and Production.
Obviously for In-House Engines., most of the Toolchains are also internally produced (and typically specialised for what they need to do) … while for Unreal Engine, well it's a bit more Generalised. This on the whole cuts down on the need for Multiple Content Creation Pipelines (primarily speaking).
What I mean is., you can craft a Characters / Environment / Vehicle Asset for UE4; then simply pull it over into Unity for Prototype Testing and it's (mostly) basically usable without another Work Pipeline specifically for it.
You're not really converting over any actual Mechanical Elements between the two.
Could AppGameKit add support for the Unreal Model Format (umodel) or Unity Model/Scene Format (.model/.scene),. eh I guess... but what would be the point.
AGK like Unity is essentially a Rapid Application Development Environment... why make it easier to use a direct competitor?
And no, of course in terms of Desktop / Console Games; they're not even in the same league … but in regards for Mobile Games., honestly AppGameKit and Unity are very competitive products.
Now in all honestly., I was for the most part unaware that AppGameKit was even capable of 3D or Desktop Development.
Everything I'd seen showcased it as some Visual 2D Game Maker, primarily for Web / Mobile Games.
On top of this, it isn't available via the Microsoft Store (Apps) but instead is available via Steam, which on it's own somewhat cheapens the impression of the product.
Not being funny but from a Professional / Business Owner Perspective... Steam Software is like shopping in the Bargain Bin at a Super Market, and when TGC/AGK Web-Presence is... well nearly non-existent, with a Website that while it LOOKS nice., doesn't really give much information on WTF the Product actually is.
When you then add to that, that after getting frustrated with trying to jump through the hoops to get the "Trial" Version... I just gave up and bought the Basic Package on Steam, just to try the damn thing out.
Yeah... that's not exactly leaving a good impression.
Especially when you can download and start using Unity 3D immediately, all you need is to create an account on the Website.
I'm aware that both products have different License approaches.
Unity 3D having a Tiered Income Royalty., where-as AppGameKit (as best I can gather) is Perpetual and Royalty Free... but to me, it would certainly encourage more people if they did both.
Sure, 10-15 years ago Price Gating made sense; as it was the common practise.
Unity 3D was £85, Dark BASIC Professional was £75, etc... but today... there are just so many alternative options that don't cost a penny to get started with.
And really if you're trying to encourage Developers (Development Studios) like myself to convert over, or encourage a new Generation of Bedroom / Indie Developers to adopt your product... well you want to tempt them in with the Core Product being Free., this might seem like a strange business tactic but once you hook people in … well then you charge for the additional / professional / team / resource elements.
I'd actually instead of a Royalty System, instead suggest a Tier Subscription System.
Say:
Core = Free
Standard = £10 / month (this provides access to the extensions, like VR, Visual Designer, etc.)
Professional = £25 / month (per 5 Seats, as Access to the API SDK, Provides Team Features; such-as GitHub and Shared Project Development)
Heck you could also have say a Quarterly and Yearly Sub that have discounts to encourage longer-term investment., with an Enterprise (50-100 Seat) for Education and Studios for a Yearly Subscription Fee.
By all means, have the Core Edition on Steam / Microsoft Store / Apple Store / etc.
Heck I think it'd be amusing to see it on the Epic Store even... but have the Subscriptions handled via the Website / Account System, that's SEPERATE from 3rd Party Systems.
Notice how nothing I've said so far has anything to do with the Product itself.
Because, really the key thing here for Product Support... is primarily awareness, image and branding.
If you don't have those... then consumer / developer support is always going to be relatively niche., and most importantly here; part of that branding and image is going to come from products that are associated with it that are popularised.
I mean, consider for the moment that the one that TGC themselves tout is the UK Driving Test App that has used Dark BASIC / AppGameKit throughout it's Lifespan.
Even within the UK... I'm not being funny, but most people don't really care too much about that... it's not a big draw.
Where-as., if there was a major (High Quality, PC / Console) Game Release that used it... well that would be a game changer (pun intended).
…
You want to put AppGameKit "On the Map" … well, that's entirely in your hands to do.
Give TGC something that they can milk for Marketing and Branding Purposes.