I like the fact the none of TGC products require a subscription but I wouldn't have an issue with paying for an AppGameKit V3.
With a cross platform language like AppGameKit, keeping up to date with all the changes to the various platform feels like a nightmare. I personally think it's a little unrealistic to expect TGC (or anyone else) to keep updating their software for free to cope with things that are outside of their control.
I like the idea of a modular approach using plugins, people only have to buy the functionality they need, but then the plugins (or extra utilities like map editors or media or whatever) need to pay for the up keep of the core product as well. If I look at DBPro, I feel that this approach has ultimately failed.
For other software I use that's comparable in cost to AppGameKit (TurboCAD) you pay full price the first time and then, as a registered user, you can buy any future update at a discount, you can even skip versions, but the license for whatever version you have never runs out.