Hi SolusIpse, nice to see you still around sometimes.

Sadly, Nspire dev has slowed down recently, because Ndless 1.0 is only compatible with OS 1.1, which has issues on newer Nspires and the even newer ones cannot be downgraded below OS 2.0. Ndless 2.0 is progressing incredibly slowly at the moment. It currently runs on OS 1.7, but it doesn't work too well on OS 2.0 yet. The developpers are busy so it hinders developpement a lot. There would probably also be legal issues due to the hack allowing a CAS OS to be sent on a non-CAS calc, so they are waiting for that and trying to figure out a way to get around that.

Right now, though, on OS 1.1, you can do ARM9 assembly and C. I am not experienced in the domain, though, so you would need to ask in this section what tools are required to make games on it.

As for 68K it seems to be slowly fading away, both due to TI phasing out 68K calcs it seems (and Nspires picking up in popularity) and Kevin Kofler trolling scared several veterans away (such as the person maintaining TiLP).

Nspire dev should pick up again once Ndless 2.0 comes out, but there are no date for this yet. I am sure they welcome any contributions, though. You would need to PM ExtendeD or geogeo on yAronet forums or United-TI.

That said, the z80 community is doing some sort of come back, especially with the new language Axe Parser.

It was, sadly. The 84+ calcs made after May 2007 only have 48 KB of RAM instead of 128. This means while older 15 MHz calcs got 96 KB of extra RAM, the newer ones got 16. Calc84 was working on an alternative but progress has been slow lately. I hope he won't quit calcs. You can check the TI-Boy SE section. You may find a topic regarding newer calcs.

Any well-behaved standard arm-elf-gcc toolchain will work for the Nspire indeed, but there are significant restrictions on what the programs can do because there's no program loader (=> no relocation support => a number of uses of global variables, or functions, is impossible).
Writing a BFLT program loader would be fairly easy (because the BFLT format is trivial), and files in BFLT format are easy to produce from the ELF output of arm-elf-gcc toolchains.

Is it still just TIGCC or did the split happen and there's another C compiler for 68k calcs?

There are two other C compilers for TI-68k calcs: GTC and GCC4TI.
GTC has a brand-new compiler that works both on the computer and on the calculators; GCC4TI is based on TIGCC, it's a superset of it and it contains multiple fixes and optimizations (some of which are thoroughly tested, and were contributed to TIGCC as early as 2002). A lot of work is necessary to raise from the arguably low quality of TIGCC (no sane build system, portability issues in the build scripts, thin test suite, etc.)
There's no sort of come back on the TI-68k community, which has been largely dead since 2007 (though several great programs, like lachprog's, have been released since then).

and Kevin Kofler trolling scared several veterans away (such as the person maintaining TiLP).

Romain Liévin left mainly because he is working on getting a higher degree in teaching physics, wanted to spend more time with his wife and children, and didn't learn much anymore (from a development perspective) from maintaining such large projects.
But it's a fact that Kevin Kofler's misbehaviour with so many people over ten years has something to do with Romain's decision, and the decision of many people over the years.

One issue with C is that it was apparently not suitable for z80 platforms. Writing a good C compiler was apparently very hard . Same for Java. It was much easier for someone to make a brand new language, or something that looks similar to BASIC but is rather simple in syntax so it can be compiled easier. Btw did you see the Axe Tribute video? Altough more have been shown since then, the video already shows a lot of Axe stuff. I myself have been working on a game called Supersonic Ball in the projects/ideas section which has parralax scrolling.

If you check ticalc.org featured programs for the last 7 months, you'll notice there are more so far than the first 7 months of 2008 and 2009 combined and I think more than 2006 and 2007 if I remember. Cemetech and Omni activity picked up, TI-BASIC Developper is slowly doing the same since the past month or so and TI-BANK has been picking up for at least 2 years. The only downside is that ticalc.org traffic did not rise that much and a lot of other forums were nearly left abandonned by their admins (altough some were hit by situations similar to KK but to a lower extent, causing some ppl to migrate elsewhere) and it caused them to spiral downwards while other sites spirals upwards.

In other words, the TI community in general is picking up again, but it would be much better if we had Ndless 2.0, even if it only supported OS 1.7, which is installable on the clickpad Nspires which are still for sale atm

I heard it produced inneficient code, as did SDCC. I never used them, though, so I cannot judge myself.

What does ISA means? I checked Google and all I got was stuff about old graphic cards and international societies/studies/etc

Aaaah ok, thanks for the info

I assume the fact C compilers are hard on z80 is because it's a 8 bit processor, right?