Is "pronunciable" or "pronounceable" more correct, considering etymology?

Pronunciable is incorrect. The correct adjective for ‘something that can be pronounced’ is pronounceable. Adjectives that end with the suffix -able are mostly formed from (transitive) verbs. In this case, the verb is ‘pronounce’:

• pronounce (verb) + able → pronounceable
• manage + able → manageable
• update + able → updateable (updatable)
• enjoy + able → enjoyable

Also note that you cannot remove the e from ‘pronounceable’ because if you do, it will turn the /s/ of ‘pronounce’ to a /k/ (*pronouncable).