Why can't we just get a skateboard?
I mean, not that I'm complaining about skates! Skates are really nice in the long run. Maybe pretty outdated(since no one I know uses rollerskates, but that's just me), but as far as a Pokemon game goes, it's not something that I'm going to complain about because the bike was kind of boring, and it was nice to have the change anyway(that is, if it happens).
And I'd say just get rid of the bike. We've had five generations to mess with it, ride around with it, and do all kinds of things with it. I mean, this is just me, but can't we just put it to rest? I suppose it would be a good idea to at least include it as some sort of alternative item for the skates for those who are still attached to it, but I feel that it already had it's run, and that we're moving on to better and better items as far as transportation goes. And then I think that after skates, we'll finally have a flipping skateboard, at least, I hope. XD
Even though it seems sexist wouldn't making rollerskates female exclusive and making a skateboard male exclusive give the game slightly more flavour? the fact that depending on which protagonist you pick male or female you get a different transport method which in my opinion would be a fair thing and would look alot better.
The bike thing though is something which 95% of pokemon players can relate to in real life, on a cold frosty day riding you bike to the shop or on a hot summer day riding your bike with your friends, how many people have those same memories on rollerskates or a skateboard? Not many I presume. The bike will always be apart of pokemon because it helped the player connect with the game easier and find it a more enjoyable experience even though it wouldn't seem like it from just a bike. Maybe Game Freak should do some new adjustments to the bikes and make them a little more interesting but as for scrapping them completely I feel they hold too much of a subliminal sentiment to get rid of.