Now before y'all jump down my throat about it, I am perfectly aware that just about every manufacturer has made a K4s. As they should; it's a beautiful locomotive. It's proportioned properly, the high drivers are quite pleasing to the eye, and as far as models are concerned, they usually can negotiate tighter curves than some of the bigger Pennsy steam, making them much more appealing to guys with smaller layouts.
That being said, I personally would like to see at least a few of the "upgraded" K4's. For example, K4s #5371, upgraded with Timken roller bearings and lightweight Timken rods. 
Other mmodifications on various engines included Scullin disc drivers, poppet valve gear, coast-to-coast tenders (which Lionel recently released, thank you for doing something different) Franklin trailing truck boosters, and "elephant ear" smoke deflectors.
Modification of existing tooling to produce these upgraded versions realistically would not be that difficult, nor that expensive. I know they can nake modular tooling to allow for prototype-specific details; Lionel did it a few years back on their version of the NYC's streamlined Empire State Express. So why can't somebody do it for the always-popular K4s (to you manufacturers out there, I smell a profit here, guys)?
Anyway, that's my bit. Didn't mean to get on the ol' soapbox.
