I just had a look at VICE again and noticed that it, while being a bit cumbersome, looks well suited for TAS.
Would you allow (converted) VICE input files for submission?
What it offers:
* Frame advance (redefinition of shortcut keys highly recommened)
* Recording input (and other actions such as inserting disks)
* Starting new movies from reset (needed for valid TAS)
* Setting a single milestone and jumping back to it (not 10 like most other TAS-capable emulators do, but it's possible to swap files)
* Rerecording a given input file at any point
In default settings VICE will record input starting from the current emulator state and thus create 2 binary files: start.vsf (start snapshot) and end.vsf (end snapshot and all input up to that point). When starting from reset no start.vsf is created fortunately, also even after stripping everything but input data from end.vsf the movie will still play (you just won't be able to jump straight to the end any more).
To make it suitable for TAS an external tool will be needed that converts the end.vsf file to a text file containing a list of input so everyone can see that it's 100% legit, also this has to strip all binaries and replace them with sha1/sha256 sums (yeah, inserting a game into the emulator will append it to the input file); another tool will then be needed to reconstruct the end.vsf file from such a text file, asking to be provided with binaries as needed, and, if possible, launching VICE to play the file just reconstructed.
This tool creation should be a straightforward task since the file format is well known (open source).
Some minor details should still be figured out. VICE allows changing hardware details; there are 4 different video standards (major timing differences) and newer chip revisions can cause minor differences. I'm wondering whether such details are recorded in an input file, just in case someone wants to play NTSC games or just used a non-default machine.
For most old games there are original images (a few cartridges, many tapes, many disks) available, cracked versions are a no-go. At least for games that only load once at startup the publicated movie should however skip the loading sequence since that can be many minutes of boring screen flicker, especially for tapes.