Neph - Don't forget Quickened SLA: Teleport, that'll do the same trick (And just FYI, quickened D-Door as you suggested would NOT, as you loose all other actions after you dimension door). Sure the quickened Teleport doesn't allow you the charge bonuses, but they still allow you the extra attacks.
Shayuri's idea seems an interesting solution, as well. Along with Quickened Greater Teleport 3/day and belt of battle 3/day, that would give you one guaranted full-round per combat (Assuming you either charge during the first round, or convince the DM to change it to the more common and sensical 'once per combat' house rule rather than "in the first round") and 6 more expendable per day.
Assuming 3 combats per day, that would be 3 times per combat that you could assault your opponent from further than your reach. Speaking of which, don't forget Marilith's have 10' reach, so people can't just walk away, they HAVE to tumble to get out of your range without provoking an AoO, which limits what they can do, AND they have to end up more than 15' from you(To prevent you from simply 5 foot stepping). And if they're powerful enough that you HAVE to full round them (IE not minions) then they'll likely be outnumbered, and the manuevering advantage belongs to the side with the greater number of pieces.
Also, keep in mind that any Opponent who's a melee fighter (one not focused on mobility such as a dervish or scout) would also want to Full-Round, it's kinda they way melee classes work unless you specifically build the character otherwise. A mage or ranged character is going to try to get away from ANY melee that attacks them, so you're essentially trying to argue that melee is pointless at Epic (Which I can guarantee you from experience is far from true)
I just don't see a lot of badguys repeatedly running away from you on every turn, and even if they do, they would have to run away from you successfully four times in a row before it would even START to become an issue (Using my assumptions above about dire charge/belt of battle/quickened teleport and 3 encounters per day) Even at SIX encounters per day (Which is way more than I would expect at this level), you could still do it twice per encounter, meaning they'd have to run on three concurrent turns. Personally, I'd go with One big weapon and four little weapons as your 'off-hand attacks'. (IE Greatsword/4XShortsword or some such). That way you have the one Two-hander for a single big bash when you can't full round, and you could view the MWF capabilities as the icing on the cake for the 2-3 rounds(guaranteed) per combat that you DO get them.
