Q: looking to buy new iMac, advice?

Apple has said nothing about any new iMacs coming up.

and we are not allowed to speculate about such things in these forums.

If you can wait until october when new macs are generally revealed.

FWIW, the current 27" iMac can be upgraded to 64GB. 

It is the only user upgrade possible for it.   Whether a new one

will have any user upgradability is anyones guess.  However, it

has been a trend as of late for Apple to produce a "what you buy

now you will need to live with forever" philosophy.

Apple only offers a max of 32GB when purchasing, but the 27" 5K iMac can support up to 64GB.  You can upgrade to that easily though the rear access panel after purchase.