Well it's just my opinion at the end of the day, do what you thinks best for your game. I no-lifed hard mode for first 2-3 weeks on my account 'v w v' and lost interest due to it not necessarily being hard. The main issue was people hoarding boss items/skilling supplies at the time, I'm not too sure about the current state of hard mode as I hardly play as is on a normal account. My main thought on being able to buy potions is that people won't necessarily need to do slayer for grimy herbs which means less slayer items like whips for example being in the game mode. Along with that, grimy herbs only real use would be to train herblore for people who want 99. If I was playing with 99 herblore, I'd invest in potions from the shop and sell them for a profit to new players who want to train efficiently. A work around for this could be having separate item ids for the potions in the shop, then making them un-tradeable. That method would be best in my opinion for you to give high level players more of a means to carry on bossing, but also stop people from capitalising on gaining cash from the shop and also making people train slayer to get those herbs for exp/potions which would result in a higher percentage of slayer unique drops. That's all just my 2 min thought process though, do as you please as I said before haha.
Edit- I focused mostly on herblore/potions as I think this would have the highest impact as a whole. I slightly agree with the other shops though, to a point.