I'm doing some humble experiences with Warlords (Atari, 1980, for arcade machines) on Boriel's ZX-Basic Compiler (yes, Boriel's ZX-Basic Compiler! \o/) - the sources and the resulting .rom file are at https://dl.dropboxusercontent.com/u/795795/retrocoding/msx/warlords_zxbasic_02a.zip (i can't attach files, sharing this dropbox link instead) (btw, i only could test on MESS, since OpenMSX i have installed is stuck on segmentation faults... :S - and weird that i can't run it decently on MSX1 emulation of MESS (but on MSX2 and MSX+ seems fine) - http://img854.imageshack.us/img854/9413/ecoo.png ) 

It is just a compiled test, not usable yet as playable demo - please take a look at the code available together as well - it's was mostly a test of what can be possible from Boriel's ZX-Basic Compiler, for an example that can illustrate a bit better than from just a mockup picture.
You actually can move all players: cursors on yellow, a and s on green, f and g on blue, and j and k on red.

thanks!