Yes, it would absolutely have a negative effect. Not only if you release an X8, but I think that creating phase-2 and/or phase-3 versions of the X16 would further dilute what an "X16" is to the layperson. Earlier, ZeroByte wrote "I never had any interest in phase 3. A Raspberry Pi running an emulator would give the same experience." and I think that he is not alone in thinking that. To further expand on that, I don't really see much point in the phase-2 version either; to me it just seems like a cut-down version without purpose.
Having multiple SKUs with differing feature sets will fracture the user base. This is already going to be a somewhat niche product, why fracture that into two, three, or even four segments? I think that only offering 3 different variations of the phase-1, the only phase, is the correct move: as a kit with or without a case, or fully pre-assembled in a case.
From my perspective, the X16 is all about learning; I think the future of the X16 will be determined based on the quality of the documentation it comes with. You want everyone who uses one, young and old, to be able to say "look at those chips, I know what every one does and how it all works together!". I think going with the vintage IBM style of documentation would be appropriate; Include three-ring binder(s) and plenty of thorough, easy-to-understand paperwork, detailing every aspect of using, diagnosing, and developing for the system. I believe having a physical copy of the documentation is vital. Having the docs solely on the internet or a phone app would be distracting. It also fits with the "Old Style, but Modern Perspective" theme.
Consider the potential users of this system. I think that the demographic is tech geeks and children. At this point you can probably stop thinking about the geeks since everyone who's seen your videos has probably already made up their mind about whether or not they will purchase one when they're ready. That only really leaves children. How will they feel when they open the box? The first time they turn it on? The first time that they look at the documentation? The first time that they need to troubleshoot? First impressions are really important, especially with children. This is why I think that having good docs will go a very long way. Of course it is possible to overdo it though; lots of paperwork can be intimidating.