heck for all we know they could throw a curve ball at us and have Ash catch a gen 4 pokemon this generation if we get the D&P remakes this generation. Now I know people like to dismiss that saying it won't happen, but keep in mind that I'm pretty sure that the writers are probably somewhat aware of people thinking that Ash wouldn't get a past gen pokemon that would advertise the current remakes at the time, so it isn't that unrealistic or unbelievable that they would give him one partly because most people aren't expecting him to get one.
Because I mean if you look at they already did generations where Ash's traveling companions were the one to get the pokemon that would advertise the current remakes, and then we got a rival that had pokemon that advertise the current remakes, so if the writers are wanting to be unpredictable we can't just assume that oh if D&P remakes come out that Ash won't get a gen 4 pokemon or that they won't bring one back, as it's really up to the writers.
I honestly want Ash to get a gen 4 pokemon if we do get DP remakes, because i'm tired of the "Oh we need to only see the new guys!" logic.
seriously since gen 5 people have only cared about the new pokemon and not the older ones anime wise, makes you wonder why the older ones should even exist anymore in the anime if the new ones are supposed to get all the attention and be shoved in our faces all the time.
When it comes to Ash, it's hard to get attached to his pokemon because if their going to be oaked, we're likely to never see em again, and he's got so many now it's hard to see him actually call them all back, the only real chances they have outside of filler arcs are leagues, and it's always debated because "Oh this team helped him here they should handle it." I think clearing all obstacles (gyms and in this case trials) is good enough for the regional team.
I know that the mindset is "oh we need to premote new stuff!" but you can still do it with the older guys, I mean heck Z-moves unlike mega evolution are practically made for everyone, so I don't see why they can't let some older pokemon get attention because of those moves.
Rant aside, I'm not happy about Rockruff(hopefully this means no Mudbray though), if Ash got one it should've been a wild one or given to him sooner, not one handed to him this long after bonding, because I feel that's lazy, you can argue Oshawott but it joined up with Ash pretty quickly, if Rockruff had joined Ash sooner it wouldn't be as big of an issue to me.
As far as water types go, when you consider what Greninja did, I can not honestly see any of the new guys topping that, so why bother? he didn't get a grass type in Kalos so maybe it's water's turn to sit out, and ride pokemon more than cover the travel issues.