Wally wasn't originally supposed to inherit the mantle. The "Flash" was at some point planned to be a new non-speedster character after Crisis. The idea to hand the title over to Barry's former sidekick was made late in the planning, I think. So, I can easily see the decision changing if Dick hadn't already shown that readers would accept a sidekick moving up.
In fact if the Titans hadn't been DC's top seller I wonder if Crisis would have either regressed or eliminated the Titans generation.