Here's the little thingy thing...
Properties were a last minute decision for GTA V single player, that's why they're so half assed. And no, these properites WON'T get any interiors with the next gen and PC release of the game nor anything else, that's how they are and that's how they're gonna stay although it's possible to have more purchasable properties with interiors and other crap via DLC
The Online apartments appeared in the SP trailer either by mystake which is unlikely or simply because they were indeed meant to have an impact on the SP as well.
Now honestly speaking, I don't want any of the Online apartments in the single player simply because they're nothing really too special, they're generic and small as hell.
The reason I wanted purchasable houses (not apartments) in SP was because I wanted each one of them to be unique, fully fledged (not just a couple rooms) and each one with an unique art style. A bunch of modern mansions on Vinewood, a couple more on Vespucci Canals, lots in the countryside and so on. The ''houses'' of Online use the same interiors as the other apartments which is pretty pathetic.
Same goes for properties, I don't just want interiors, I would want more substancial content coming with each property, maybe developing like a little career with each bussiness/property and having to do something for them not just buy them and then receive their revenue while having some perks.
Like running your own drug dealing ''bussiness'' and having to take care of it, make deliveries, attack your rivals, organize robberies to steal their drugs, etc and all as a side thing
Or buying a club and being able to manage it like in the TBOGT DLC or hire somebody who needs an actual salary to work in your place when you don't bother
Or buying a restaurant and having to deliver the goodies yourself or again hire someone up and then having to protect it from gangs coming to mess around
You know, that constant feeling that you have to do something for your sh*t, that you're an important person, so important you randomly and dinamically have hitmen after you trying to get your head, getting into your house, having to constantly protect your family as Michael or again, hire up bodyguads to protect the house.
But nope, go play Tenis, Golf and Yoga instead, they'll be better than all that stuff.