Should I buy a new Retina MBP now or wait for update? Will the difference be truly worth the wait? Due to Intel's uncertain roadmap for portable chips, I'm not sure if the update will be coming up in May or closer to Fall 14'... 
Just buy it now.
No one - perhaps not even Apple - know when they'll be updated.
Should I buy a new Retina MBP now or wait for update?
What update? It's all guesswork right now. No-one knows when or what we'll get.
Although I have a Haswell 13" rMBP, I also own a first revision 2011 15" rMBP and, so far, haven't updated it and, you know what, I'm not missing out a great deal? Slightly better battery life, but after reading pages and pages on how the Haswell MBP panels were so poor, I'm happy to keep my first revision 15" rMBP. An "upgrade" doesn't necessarily mean "better laptop".
I ended up pulling the trigger, as my 2011 MBA (already sold), wasn't cutting it anymore. Hopefully they have solved the panel issue now that its been 6 months after release and I'll get a perfectly good panel... regardless if it was made by LG or Samsung.
Buy now, ebay later. If Kuo hits the nail, the next Haswell (slight) speed bump will be around October after the iPhone 6 and the more significant Broadwell refresh will be Spring next year (this will be totally up to Intel's delays).