It's not really that hard, just keep the original HM's from GSC, flash cant be traded because it would be a HM, it would mean that rock climb and defog would only be obtainable through a move tutor or through DPPt but to be honest who really gives a dam about them anyway, its really not as complicated as some of you are making it.
They'll introduce whirlpool back but maybe have rockclimb as a TM for the sake of it.Defog could be put into use if they fog up the whirlpool islands,but i see the original G/S HM's all coming back ..
Okay, like Hiroshi mentioned, the games won't be exactly a 1:1 ratio as the originals. There
will be changes to the remakes other than just new features. Before when FRLG came out there wasn't as many changes within the Pokémon games, until DPPt came out. This is when things became more complex than what they were a few years ago. A lot of you say it isn't hard, but if you think about what you may say, such as make Rock Climb a TM, then you are making it more complex than it is.
For one, and I don't know how many times this has been stated before but HM Flash will not make a return, as DPPt has already made it TM for the games. Seeing as the remakes and DPPt are all compatible, this only reasons why Flash won't be brought back as an HM. Also, the idea of making Rock Climb a TM won't work because again, when it comes to trading in DPPt Rock Climb is known as an HM. So, if Rock Climb happens to not be brought in as an HM for the remakes, then it'll be available through a Move Tutor just like how Dive was made in DPPt.
Also, Whirlpool, this can easily be made an HM. There will be no trading so cross compatibility will not be a problem. However, Defog can easily replace HM Flash's position as it won't be difficult to replace the black cave areas to be filled with fog. Yes, it may be a useless move to teach a Pokémon, but it is used for the difficulty of obstacles within the game. As for the other HMs, it isn't hard to make Rock Smash more of a vital move than before and it isn't hard to accomplish the other HM's uses either. However, as it goes for Defog and Flash, it is simple enough to keep Flash a TM like in DPPt and still have little use of it; while all the less, it is still possible to replace the dark areas and fill it for fog to take use of the HM Defog. Nothing is ever complicated unless you break it down and look at all your options and what you know can and can't work.