It is quite a surprise that Wave 4 has arrived earlier than expected, as it had been updated into Mario Kart 8 Deluxe on March 8th in certain regions (For instance, the update came at 5 PM Pacific / 8 PM Eastern in the United States.), rather than March 9th.

This is because at the time of those region's time zones, Japan's time zone is March 9th at 10:00 AM.

Still, nevertheless, we now got our next wave of tracks & Birdo has now become a playable racer.

There weren't too many issues with the tracks in Wave 4. 

My only issue is with the section of the Bangkok Rush where the Inky Pirahna Plants should be, as they are now replaced with generic Pirahna Plant sprouts which may not do anything to you unless you run into them by mistake (unless theres a barricade preventing you from running into the Pirahna Plant sprouts).

Anyway, what's more is that we finally have an idea of how more characters will be updated into Mario Kart 8 Deluxe.

As you see in the image above, the character roster has now been currently updated into a 8 by 6 layout - 6 rows with 8 characters each.

Underneath Birdo's column (as she is show in the 1st row of characters along with Mario, Luigi, Peach, Daisy, Rosalina, Tanooki Mario, & Cat Peach), there are currently 5 ?'s (Question Marks), currently showing there will be 5 more characters to be added into Mario Kart 8 Deluxe via the Booster Course Pass.

But who will those 5 characters be? For now, it's a mystery. But you can be certain that I really hope so very badly that one of those mystery charactsrs will be Pauline.

And although it may not be likely, it's possible that the character roster and the 5 mystery characters may be subject to change, thus why I have put emphasis on the word "currently".

For one thing, it's possible that if the Booster Course Pass ends up being a success, Nintendo may do even more for Mario Kart 8 Deluxe than we might realize. Perhaps when a good amount of time has passed after the day Booster Course Pass ends, Nintendo may add even more characters, vehicles, tracks, & other content into Mario Kart 8 Deluxe. After all, with all the sales numbers, Mario Kart 8 Deluxe has become one of the most top selling Switch games of all time, perhaps even the all-time top.

After all, Super Smash Bros. Ultimate, as well as its predecessors on BOTH the Nintendo Wii U AND the Nintendo 3DS, had TWO DLC packs; so maybe Mario Kart 8 Deluxe could end up having a 2nd pack of DLC as well.

But keep in mind that what I've said above 2 paragraphs is only a possibility, NOT a guarantee.

Needless to say, we still need to spread the word to everyone, especially to Nintendo, that Mario Kart 8 Deluxe should receive even more characters tham just Birdo & the other 5 mystery character (EVEN if one of them ends up being Pauline),  along with more vehicles, wheels, gliders, power-ups, & other content.

For not only does that justify as a means to preserve Mario Kart Tour's content when it discontinues...

...but remember those cameos of thw Flame Flyer & Royale from Bangkok Rush? Well, those cameos have been RETAINED in Mario Kart 8 Deluxe's version of that track, just as I predicted all those months ago.

That means when Mario Kart Tour discontinues, Flame Flyer and Royale will be among the mant vehicles, along with characters, wheels, gliders, power ups, & other content, that will not only be lost forever, but also be rendered unplayable in Mario Kart 8 Deluxe UNLESS Nintendo updates said content into the game.

And let's not forget other vehicles like the "Super Pipe Frame" (the cubical engined, dual exhaust piped Pipe Frame from Mario Kart 64 to Mario Kart 7), as well as the vehicles from The Super Mario Bros. Movie, which will have its final trailer showcase in the final Movie Direct on March 9th.

So until further notice, let's keep at it with spreading word on our hopes & desires for new content for Mario Kart 8 Deluxe in any way we can to everyone, especially Nintendo.

Good luck.