but i wouldn't rely on "hacks" for commercial products
Its not rocket science or voodoo. The source code is available as required (xc16/xc32), and if you can read code there is no mystery what is happening. The compiled code is exactly the same as the 'paid' version. Exactly. Always. There can be many reasons to go for the paid version (priority support would be one), but to think that you are getting a more 'reliable' compiler in the paid version makes no sense. You don't even need to 'hack' any file to get all optimizations/enable c++.
I think the OP is not interested in xc16/xc32, so it doesn't matter anyway.
and the latest version of XC32 bundles both MIPS and ARM compilers
They have 2 ARM M4 crypto controllers- which seem to have no home, so they adopted them in mplabx for some reason. Maybe its a test run to see if they can make arm work in mplabx.
Whatever they do with AS/MPLABX, its not going to happen quickly. So unless you want to wait around for at least a few years, plan to use what is available now.
You can also look into the mchp 8bit parts (newer ones with pps are nice), then you can use MPLABX instead of AS. The xc8 compiler (not open source/gcc) in free mode is restricted in some optimizations, but it is not a big deal (at all). They have a $30 Curiosity board which can mount 8-20pin pics, includes a programmer/debugger, and works quite nicely. I guess it depends how attached you are to the tiny24. Just a thought.