Currently, as far as I'm aware, new players have access to all shift stones from 0 BP, including many which they cannot utilize due to lacking access to the moves required to utilize them at pebble rank. I think it would make sense to only have unlocked as a pebble the shift stones that don't require a certain move to utilize them and to allow the shift stones that require certain moves to be unlocked only once the required moves/BP has been acquired. Since there is a shift stone tab in the gear market, perhaps they could be acquired from there once the player has those moves and/or the required BP?
Rank (BP) requirement for each stone with this change:
Pebble (0 BP) - Surge, Adamant, Vigor, Guard
Tor (30 BP) - Flow, Stubborn [this rank grants Dash, which completes the set of two moves referenced on both of these stones]
Monolith (96 BP) - Charge
Mountain (156 BP) - Volatile
Thank you for your consideration. ^_^