Propably said million times already in this thread. Effects to my single player game are limited only to the multiclassing rule changes.
Other changes are not even worth discussing.
Multiplayer changes the spell level change (if makes to release) will be visible in my game. Thus it should be at least an option!
Do you mean that if you multiclass you will feel the effects of this ruling, which is a fair concern, or that enemies will have it? Because in the latter I'm pretty sure it has always been like this. There is nothing in 5e that prevents from building a caster statblock with both mass heal wounds and scorching ray. Casters statblock don't even have spellslots, they just works differently.
