Now that we've got a pretty extensive look at the game and what it offers, how much do you predict it will sell lifetime, and why?

The highest selling game in the series is currently Donkey Kong Country on SNES at 9.3 million, followed by Donkey Kong Country Returns on Wii at 6.53 million.

I believe 15 million is doable

While Switch 2 just came out, it is the fastest-selling platform in its first 4 days ever. That bodes well for the "Switch Effect" continuing with software.
DK is no Mario in terms of popularity but is nevertheless iconic. I put the 10-12.5 million range. It helps that it is such an early title in the console's life, preceding juggernauts like 3D Mario, Animal Crossing, 3D Zelda, Smash, Pokemon Gen 10 etc.
I could very well see Bananza as one of the best-selling 3D platformers on Switch 2, only exceeded by the 1 or 2 3D Mario games that will be on Switch 2. I don't even think a new 3D Kirby game would outsell Bananza.

10-12 mil

I’m going bold: If LM3 could pull >15mil, then there’s no reason DKBananza can’t cross 20mil on a system likely with 8y in its tank.

I think it will break Donkey Kong records sales wise. As long as the reviews for it are good I can see it hit 13-14 million.
It is a game that appeal to several different gamers, both DK fans, Mario fans and I think the sandbox game gang will all check this out.

It for sure is the game to pick up after Mario Kart World for Nintendo's new system.

I think it could be a Kirby forgotten land or Luigi's Mansion 3 style hit for Nintendo, which would be a massive boost for the Donkey Kong IP into the future.

Bananza releases with a number of advantages:

1. It's coming early in the life of a new console.
2. It's published on one of the most desirable video game systems ever.
3. It's a top shelf game...
4. ...that also happens to be in a genre that is lucky to average one such release per year across all gaming platforms.
5. It's Donkey Kong, one of the most recognizable video game characters in existence.

Shipments could look something like this:

4m in CQ3 2025
4m in CQ4 2025
4m in 2026
3m in 2027
2m in 2028
1.5m in 2029
1m in 2030
1m in 2031
1m in 2032

I expect its legs to gradually decline because eventually there will be a new 3D Mario game on Switch 2 which is more likely to become the first choice for new Switch 2 owners when it comes to 3D platformers.

Unsurprisingly, I voted for 20m+ in the poll because that's what my numbers add up to.

For reference, the low-advertised Switch 1 port of Donkey Kong Country: Tropical Freeze reached shipments of 4.62m by December 2022. Kirby and the Forgotten Land's LTD shipments by March 2024 were 7.52m, which marked a new record for the Kirby series; estimates put it above 8.0m by March 2025.

The sales of this are going to be bananas.

Really difficult. Im guessing 7.5-10M.