No way man. It's more complicated and unnecessary to have one class which has two entirely different spell tables, than two just have two classes, which also would let you bring Warden back, and designing it so just one subclass of many uses the "default" spell table, and all the other subclasses use the "extended" spell table is
literally perverse. It'd be fine if Moon Druid had a special spell table which was like a variant half-caster, I guess, like it hits 3 and doesn't progress on spellcasting again until it gets to the half-caster equivalent of 3, but why not just bring in a nature half-caster so you can get Wardens in? They'd fit well with 5E I think. Or just make Moon Druid into "Moon Ranger" or whatever, if you must. PS I like Wardens.
Also 5E's multiclassing is a crime. You don't answer one crime by going "It's fine let's do more crime!"