Most likely we'll get the exclusive box set that everyone wants but can't afford which will have the BluRays only. Then individual BluRay/DVD combos then individual DVD releases with little to no features. The latter I'll probably go with unfortuantely because A) it'll be cheaper and B) I don't own a BluRay player. Is it me or do BluRay/DVD combos sound pointless?? If we own BluRay players why would we want the DVDs???
I'd say it depends on how they choose to release and market them. If the Original Trilogy is marketed as an alternative cut along side the SE in a premium box set, then the odds that there will even be a DVD release of the OT are pretty slim. A lot of premium extra content including alternative cuts of films are Blu-Ray exclusive these days, so I could imagine there not even being a DVD release of the OT at all, just the SE. If you look at Disney's current releases now, assuming they would be the ones distributing this release or even Fox, most often they will include all of the substantial extras on the Blu-Ray only, with a few measly features tacked onto the DVD. Even with Fox titles and alternate cuts (which the OT might be marketed as alongside the SE) the DVD usually only includes whatever the main version of the film is considered to be on a single disc with little extras.
Now assuming this could be a different scenario where the SE gets phased out completely or at least aren't focused on or included in this release, than yes, there would be a better chance they will be released on DVD if they are considered the main presentation, but it still definitely wouldn't be a guarantee that the OT would be released on DVD at all. Afterall, There still is no stand alone DVD of the 2011 cuts of the SE on DVD.
Honestly in my opinion, The whole Blade Runner scenario with all of those multiple releases at once on multiple formats wouldn't happen today the way it did in '07 as far as a concurrent release of the same content on DVD goes. The market has totally changed and studios no longer care about DVD. Blade Runner came out at a time when Blu-Ray's potential was just really starting to take off, but DVD was still a big player in the game and was what a lot of people were still buying at that time. Now, DVDs are mostly an afterthought with little to no effort put into them, so I would be hesitant to assume that there would even be an OT DVD release at all if this whole thing does actually happen.
Also, I'm don't exactly know what your reason is for not owning a Blu-Ray player, lots of people still don't and I have nothing against people who chose not to embrace the format for whatever reason and there is nothing wrong with that, but honestly you can get one now for about what you would probably pay for a theoretical OT box set when it's released, or probably even for less if you really want to enjoy all of the bonus content and what not that will most likely be exclusive to Blu.