"the Flex 5K will likely not see new features in PowerSDR unless they come by virtue of updates really targeted at 1500 & 3000 users"
Whats to explain? Do you know of any new development specifically targeted at new features for the 5K? Unless the price is dropped significantly the 6500 will likely be the mid range radio. The lower models have a different price point that will allow them still to be viable selling products for a little while longer. Still though, I predict we will see more compettion coming soon that will make those less attractive.
As an SDR the Flex 5K has pretty much matured, it has the basic software covered and is end of marketing life. Most Flex 5Ks sold now will be on the used market.
Of course this is merely my humble opinion and not based on any facts.
As a current active Flex 5K user I am not really expecting anything new for that radio.
If I can ever afford one on the used market, I would truly like to have a fully decked out 5k including the VHF/UHF module. It's ashamed they could not keep producing those. I know they were criticized but I believe it was some sort of parts supply issue that bit them. I still like the concept of an all in one rig that covers up into the uHF range. I had a TS-2000X which actually covered 1.2 Ghz as well. It was a nice radio except for the birdies.
Speaking of VHF/UHF coverage though, is the 6700/6500 going to have the ability to use transverters in a full duplex configuration? Seems like it would.