They can't combine the techs??? That was the point of developing IS OmniMechs in the first place. Aww well, that balancing issues. IS Mech are were historically boweled over anyways
even with clantech being adjusted in the 'intangibles" to be more even vs IS tech, IS mechs using clan tech would be too disruptive to the game balance. so they chose to keep the tech bases seperate.
and btw, the reason for making IS omni's in battletech had little to do with using clan tech.. it was all the advantages of omnimechs in terms of logistics and role flexibility that sparked it. the ability to pod mount clantech was just a handy bonus. (and remember, the plans LAW gave to the other states for things like the firestarter omni and blackjack omni didn't come with clanspec compatible connections alongside the regular ones.. that was something LAW kept to themselves. makes it unlikely using clantech was considered the main reason, if the default design can't even use clan tech.. )
as for IS mechs being bowled over.. yeah, in tabletop BT they were. but most of those were 4th succession war tech 'stock' designs.. a single twelveman in MWO is often using way more DHS, XLFE, endo, Ferro, and advanced weapons than the typical IS
regiment had in the canon early invasion period. the typical MWO mech build has way more in common with the mythical "Mk1 clan Omni's" than with the IS mechs of battletech's clan invasion period.
that is one of the reasons i suspect that clantech won't be as over powering as people think.. i mean, if the IS had the kind of teched-to-the-nines ubermechs we say in the jihad, that rock endo, XL, DHS, and advanced weapons all in one frame, in a widespread fashion during the arrival of the clans? the clan's butts would have been kicked hard..