Looks like due to google remapping email headers and some changes in gentoo 
infra my reply did not get to the list. So, here it goes again, now avoiding 
gmail :).
BTW, there were a few posts on this topic in the linked thread on Donnie's 
blog since my last post attempt.

On Sunday 05 December 2010 13:55:40 Kacper Kowalik wrote:
> Again, for the reference and starting point for the discussion
> Donnie's blog post:
> http://bit.ly/dLwdFe
Very interesting - that this point started coming up in multiple places 
lately. I guess "the time has come" finally.  

My interest/"involvement" here is that Ada has been implementing such a system 
for many years now (perhaps the first such miltiABI class in the tree), 
therefore, if there some technical issues that can be referenced:
http://www.gentoo.org/proj/en/prog_lang/ada/dev_reference.xml
(unfortunately incomplete, but I should have put principal points there before 
"dropping it") and discussed.

The implementattion is somewhat along the lines of "2." point in thatDonnie's 
post. In fact, 2 and 3 follow the same principle, the difference is only where 
the multi-build control code resides - in the ebuild or external script. The 
Ada implementation places it in the "standard" locations: an eclass for 
building compilers, an eclass for taking care of libs and eselect module "to 
rule them all". There is even an option of selecting "primary" profiles - the 
ones for which libs will be built, and having "experimental" - just for play 
compilers. Therefore I would suggest to interested people to look at the 
code/contact me, etc.. I think we can all benefit from discussing this topic. 

Overal though, I would very much like to push for the standard "in portage" 
treatment of multiple ABIs - at leas for PM providing some necessary 
"core"functionality. However this is still not out of the design phase, as I 
understand..

George