Ok, gotta say that Splash Mountain is my favorite ride since i was 3 years old, im 25 now. So I will miss it.
I have also actually watched the Song of the South movie. I am totally fine with a change to the ride. I would have preferred a new show based on just the animated characters to then update the ride, but whatever.
Princess and the Frog is fantastic and the only thing i would prefer over it coming in would have been a new original ride theme. I love classic Disney Animation, and anything promoting the old 2D style is a massive win for me.
In terms of theming fit, I really don't think it is going to feel out of place in MK. Tom Sawyer Island, Liberty Square, and Big Thunder Mountain all have very different core location themes, but they all fit. Bayou/Swamp theming is close enough that i really dont think it will be an issue.
To be honest I think the Bayou theme fits in great or at least ok with Tom Sawyer and Liberty Square.
And TBH, i always felt that Frontierland had pretty weak theming anyway. Liberty Square, Sawyer Island, Liberty Tree Tavern, and Haunted Mansion all have far stronger external theming than the exteriors of the Shooting gallery, Diamond Horeshoe, Country Bears, and Pecos Bills.
Big Thunder has great theming, but the WDW version is easily the worst version right now. It needs love.
So to me, changing Pecos Bill and Diamond Horeshoe into southern influenced food and just changing the signs/names is easy. The shooting gallery is kinda not important, do whatever.
The only 2 things out the entire stretch from Haunted Mansion to Splash Mountain that are not easily and cheaply fixed in terms of theming are Country Bears and Big Thunder. However, Country Bears really only needs an external building cosmetic like the restaurants to work well.
Which just leaves Big Thunder. The WDW version needs love anyway, i dont want them to change it, but if they ever give us the updated effects like in DL, i could see some very minor Aesthetic tweaks to make it fit more seamlessly while still keeping its Western Railroad theme.
I am excited for this. Tower changing into Guardians was weird, But Mission Breakout is easily the most fun i have had on an attraction. Malestrom was interesting, but it scared me as a little kid and the Frozen ride is more fun but less unique.
The next ride i see getting cultural changes is Jungle Cruise. That one i always thought was the one that would happen first. I vote Indiana Jones on a world trekking journey if it has to be IP.