I like the Planetside idea... but...
my idea of my personal ultimate mechwarrior game?
A new version of Mechcommander, including Mechs, Arial Assaults, Infantery and all that. The game would be Turnbased, but allowing you to plan out turns ahead of time, and then playing it in Realtime. Or the other way around... having the option to pause the Realtime to plan.
A tactical depth to it in a magnitude of at least Company of Heroes standards... perferably more so. And some really nice graphic in the magnitude of Company of Heroes... making it seem like some Minature gaming coming to life or something. So when you pause you will have amazing Stills to watch.. with great explosions and all that... basically like CoH.
And since it all is just wishful thinking, i would love to see it in a really huge scale. Giantic Playfields... maybe a whole planet, or at least a whole continent. Maybe of the size of the american (from alasca all the way down to the south) in real scale. Allowing you to wage war in a real scale of a battle.. with all Rules of Engagement active.
Maybe starting out as small Merch unit... and then being able to bring in Technicans to salvage wrecks and such, maybe even put them on a truck and take them back to base. Having to move bases and such.
Preferably it would have a "World generator" Generating the world you play on... setting the difficulty by choosing what you plan to do. A small group of Mechs vs a whole invasion fleet... would be much more difficult than selecting to have an established foodhold with regular Ressources.
Maybe adding something some strategic objects to the map. Like a Spaceport or refineries... ammunition bases and such... stuff you can raid and if you manage to hold them, you can restock your ammunitions and such, otherwise your dependant on maybe some few drops, riskin your dropships, and salvaging left over ammunition on wrecks.
Hell... i would want a full combat simulation.
And sure... why not adding the option to designate one Mech as your own.. and, much like it was in Spacehulk, command your forces from a mech. Adding the element of having Commando-Assets into the game. If you drive a Commando-Tank you would get much more diverse tactical informations, otherwise you are dependant on stuff like having to camp near a city and sneak into it to get information of enemy positions and such.
My ultimate Mechwarrior game would truely be a fullscale Battletech Simulation. Being played either from a purely strategical point of view, being a general in some headquarters and ordering people around.. like a RTS or TBS... or going out as a Pilot and then having to either step into a Elementalsuit, go on to pilot a vehicle or a Battlemech... or taking a bunch of bundle explosives and a rifle.. and take on those mechs without any armor.
But most of all... i would love to finally see mechs having Hands and being able to use them. Pushing a button and changing the firing button from shooting your LRM to punching.