I would absolutely positively buy a Warlords update with internet and local download-play multiplayer. Even a pretty direct port of the (perhaps rare?) arcade version would be awesome. I remember the graphics in that version being pretty good, certainly way better than the Atari version. What I wouldn't want to see is some abomination involving screen scrolling. Make the game fit entirely on the screen, I don't care how small they have to make the sprites.
Major Havoc would be cool too. Since all these games are pretty simple, it ought to be a collection. Gyrus, Tempest, Tempest 2000/X3 (though it never used a paddle as far as I know, it would certainly be better with one), and Warlords w/wifi. I'd buy it!
EDIT: I hadn't known that Tempest 2000 was ported to the PS1. I'm going to have to try pick that up. I loved the Jaguar version back when I had a Jaguar. Indeed it was probably the only game to love on the Jaguar....