WDI were pushing to have it open upwards of six months earlier than they originally intended. I don't know if they received approval for this, but it seems like they got approval for SOME unspecified earlier date. They're moving very fast, even on the interior. I wouldn't put money on it (though to be fair I wouldn't anyway as I don't gamble even with safe odds), but a summer opening seems within the realm of possibility at least. Just don't plan a trip assuming you will get to ride it.
I can vouch for there being a legitimate push to get this done earlier, that was information told to me prior to D23. As for technical difficulties, anything is possible, but I do think it'll probably be less problematic than a new build. The most trouble they're likely to run into will be show elements. The ride system is repurposed, so there shouldn't be many problems there that didn't already exist for Splash. Of the AA's, probably Louis has the most potential to cause issues given his size and customizations. At least compared with the smaller animals or standard human figures (which have the same tech as those in Beauty and the Beast and Hong Kong's Frozen from what I understand).