There have already aware and answered this question (both script size and map size) during blizzcon. You can check the transcript in the panel coverage. Bumping it is pointless and waste everyone's time
Its not like they CHOSE to restrict us to 256x256 maps and 2MB code size/heap and stack size. Those are technical limitations. Extending those is hard. Very hard. Most likely, theyll have to redesign the modules that need to be modified. Maps bigger than 256x256 might even require blizzard to adjust some file specs. And theres backwards compatibility and all that stuff you have to keep in mind. You can complain about it all you want, but unless blizzard run into those problems themselves, i think theyre very unlikely to do anything about them.
I'm pretty sure their code is well designed to accommodate a change such as bigger maps "easily".
A bigger issue for them may be the player hardware requirements. A 512x512 map implies 4 times the memory usage and probably a lot more processing to track everything going on. For such maps to be playable on most machines, they may need to further improve the engine or raise the SC2 minimum hardware specifications. So I think these limitations are probably much more political than technical.
Edit: Also, 256x256 seems plenty big enough to me. It's huge even for 8 player games. And if you are trying to design a RPG within SC2, the map will just never be big enough. That would require an engine able to load terrain in chunks rather than all of it, and the SC2 engine wasn't designed for that.