From the information I have read so far and heard from European customers who have already bought an V8xx, it appears to be a classic Epson minimal update with some repackaging and a once-again vague set of marketing materials that make definitive comparison difficult.
I think this upgrade is similar to the update from the 4490 to the V500 to the V600 to the V550. Those had a updated shells and things like social media options but from what we could tell had the same basic scanning hardware except for the relatively easy to switch out from CCFL to LED in the light lid. If one is on a tight budget for scanning medium format, for the money, the refurbished V500 from the EpsonStore's clearance center is the best deal out there and produces scans just as good as the 600 and 550.
While some of the marketing materials leave open to interpretation whether the optics of the V8xx have been upgraded, I have not seen anything definitive and would be surprised if Epson went to the expense and effort to do a full optics upgrade. Moderately priced scanner optics have not seen a big improvement for years. If Epson did invest in a new optics system, I think that would be the headline on all their marketing materials. I have no doubt that scans from a V8xx will probably show to be a bit sharper than a V7xx in a well controlled test but I would be willing to bet that is down to getting the film flatter and in the correct plane of focus versus better optics. The less-diffuse LED light source may produce a bit more contrast too. Customers of mine have been seeing the advantage of flatter film and precise height adjustment for quite some time.
I have been offering my more robustly built BetterScanning.com holders with ANR glass (real glass versus the ANR plastic used in the "upgrade" offered by Epson) and step-less height adjustment for years. Epson got someone to reverse engineer a new set of holders to try to mimic the advantages I developed for my holders. If, as they say, imitation is the sincerest form of flattery, I guess I should be flattered.
It is unfortunate to see they downgraded the Silverfast software from the Ai version with the top of the line V8xx but I am sure they are trying to wring out as much profit as possible as they try to extend the life of their initial investment. These V7xx/8xx scanners are still great to have as an option for medium format and large format shooters who want to buy new but can't afford to jump up to the next class of scanners. If Epson starts offering great prices on refurbished V7xx scanners like they have on the V500, that could be killer option.
Doug