i know the batteries can be replaced but the developers clearly didn't have that in mind and not everyone has access to that info. plus, the battery replacement process isn't even something THAT easy to do as you can easily damage the cartridge.
The only things that were relevant to the internal clock in RSE were Berries and Espeon/Umbreon. Since no one plays RSE competitively anymore outside of simulators, and you can't even obtain Eevee in RSE without trading, the loss is minimal.
as far as i can see, the biggest issue would be the fact that the region of kanto by itself wouldn't create much of an impact regarding nostalgia and a new adventure in a region so overused would, almost certainly, not be profitable enough to make it a good alternative to a new gen or a simple remake.
also, taking into account they base their regions on real areas, the ammount of work they'd have to put in creating your idea opposed to a brand new gen would be essencially the same (new region since there's almost nothing to recyle due to the console transition and graphic differences already shown by x/y, new characters, new plot, etc, etc), which only reduces it's viability even more.
simple remakes on the other hand leave the developers with something to work with giving them a headstart, allowing some development time and money to be saved.
lastly, unless they master the dev-kit for 3ds by the time they truly finish this new project, i don't think they'll go with remakes that soon.
but 3ds has been around for a while now and i suspect they started working on the new gen far earlier than what most ppl would expect.
reason why i don't believe we'll get short/poor games when it comes to content like some suggest, even with the huge leap from DS to 3ds.
They did create a fairly good new adventure in Unova with a few changes.
Anyway, I'm 100% sure Kanto won't be remade, because it's already been remade.