Rubio isn't a "stud" defensively although he gets a lot of steals by jumping in the passing lanes & he sucks at finishing at the rim on top of his shooting. He doesn't fit the Spurs system b/c the offense is either going to run through Kawhi/LMA w/ the starters or motion offense w/ the bench, his inability to shoot would make him a bad fit for either one ala De Colo.
In any case, there won't be any starting PG tier acquisition until 2018 unless Tony raptures his achillies. Until then the only I can see happening is bringing back George Hill to play backup in 2017 since Patty will be a free agent then maybe go after Chris Paul in 2018 (he'll be ring chasing like Kidd) when Tony will hopefully retire (but unlikely since he want to play 20 season
).
I'm hoping they draft Gary Payton II to play the CoJo role b/c I don't see PATFO splurging on a PG this upcoming summer but rather replacements for Tim/Manu.
Ideally, Tony accepts a backup role in 2017 (Patty will be a free agent) & they sign Jrue Holiday (he's the same age as Kawhi). Jrue is a big point guard & can actually play alongside Tony without it be an issue on defense. If Tim/Manu retire this summer then they are going to have to sign salvage players like Noah/Mayo to a 1 year contract then dump Diaw's partially guaranteed contract to maintain a cap space for a Jrue tier player 2017. Most likely that won't happen b/c players with market value won't sign a 1 yr contract without an option which will cause uncertainties thus the most likely course is going after George Hill in 2017 to replace Patty then Chris Paul in 2018 to replace Tony.