It isn't only about multi-monitor displays or DX6 limitations. - Having lived with DA for some time now it's difficult to deny that watching MA cloned on two screens does emphasize the pacing back and forth feeling of the MA fish movements.
(Beautiful though the fish are). - But even on a single monitor, the variety of tanks, and fish behaviour, afforded by the competition (even Goldfish and Sharks, but mainly DA), is now showing our favorite MA in a poor light.
If I have got my estimations right, it is now over 4 years since what will be V3 (ie the 3D background), was first mooted. I know it is pointless asking for even the vaguest of ETAs, - but the natives are getting restless, - And from the above comments, it isn't just me!
In some ways I think I would prefer to be told that what we have now is it! And that MA will receive no further development, - rather than prolong this discussion through more
years of promises and waiting! ....
Life is too short! - We're getting old! 
... However, if that is not going to happen,
(at least not yet!), and I don't see Prolific getting their finger out and doing anything to improve the MD implementation,
(they're still advertising the DVD !!! - the same one that was a discontinued item when I bought it on the 16th December 2003 !!!), - then perhaps all we can look forward to is something in an after life!
... At least this forum does have its moments, on occasions!