Independance Wars and IW2 Edge of chaos both have newtonian physics, and they are great (open ended, good combat model).
I too am a great fan of newtonian physics, but I am not sure it would work that well in a mech game (as it would imply that there would be no cap on speed, except relativistic speeds).
Maybe if there were a way to charge at a mecha: that is, to deliver a blow when both mechas "cross" each other (instead of having to wait for your turn to do so, which makes it nearly impossible to melee). Such a blow would get increased damage depending of the relative speed of both mechs (that would make melee in space like medieval jousting: it would be harder to connect than "normal" melee fighting, but more damaging).
Melee in space would be hard in a "realistic mecha game", as it makes straffing much easier, but then, it would be hard to aim anything (as your speed is not capped, there is no reason why both mechs would not run at mad transverse speed, or close in at 30.000 m/h which would makes it impossible to aim correctly), thus only missiles "would" be accurate (unless the targetting computer is insanely powerful, but then, it would never miss during battles that would not occur in space).
I would much prefer to make some compromise with realism, as melee fighting is cool (and shooting something else than missiles too). It could be done with space nav computers (like the flight assist in IW), that could compensate the ennemy dodge(that is, there would be a close in command in addition to the normal move command), or something like that (maybe a motion prediction skill, or simply space fighting).
