A88: Spontaneous Clerics?
Its clear from UA page 48 that a character can be a cleric 1 / cloistered cleric 1 or a Wizard 1 / Domain Wizard 1, since these variants "are wholly separate from the character class." The specialist wizard variants are clearly a 'class feature' variant since, "a character cannot, for example, take a few levels of conjurer using the rapid summoing variant and then 'multiclass' into regular conjurer levels." (page 59)
But the Spontaneous Casting strangely has no such restriction. So is it a seperate class? Since the spellcasting is explicitly said to not stack this seems to indicate that they are sperate classes.
Q95: So is spontaneous cleric 1 / cleric 1 legal?
Wow... what a messed up can of worms that is. I'd never actually read that section carefully, and had just assumed that you couldn't multiclass between any variants of the same class. However, that is explicitly not true, as spelled out in the link you provided (I'm going to repost the text below).
Multiclassing And Variant ClassesUnder no circumstances does spellcasting ability from multiple classes (even variants of the same class) stack. A character with levels of bard and levels of bardic sage has two separate caster levels and two separate sets of spells per day, even though the classes are very similar.
I think it is certainly totally fine to let them stack, because of the underlined sentence. I'm not sure what the RAW or RAI are, though, as I don't see "wholly separate from the character class" defined anywhere, and the meaning is not clear without a definition, IMO.