As a (very) end user, who is really happy with his (almost) out of the box so far nicely working U2, i must say: Even with a dual head of another company (The Kraken) i would be happy.
Bought my U2 with the expectation/plan of getting a dual head, after a learning peroid of using the machine, as soon as it would get in store. This was (with no need) announced last year already for july 2014. The ONLY thing i begin now (more and more) to miss is the possibility to print supportmaterial for wellknown reasons.
As i plan to start a (small) business i probably need to get another printer for prints with overhangs now, right? The earlier mentioned Orcabot XXL would be (by quality/price) probably the nextt option, although the Mendelmax 2.0 in combination with The Kraken would be an alternative. (?) Yes, it is a quality/budget issue...
BUT i would rather just see a dual head The Kraken see in my (first) U2, even if this means a watercooled "solution". Really not possible/realistic?
Your postings regarding a dual head engineered by yourself seem/sound to be kinda in a dead-end street. No offence.