Be aware the images and info below may be out of date, the most recent version will always be in the 5eTools Collection (See Homebrew).
While I like the concept of the Combat Wheelchair (v3 here), I don't necessarily agree with the execution. There are some odd choices and potential balance issues I disagree with (e.g. a base speed faster than most races or a 2d6 weapon that doesn't require hands or proficiency and also gives target disadvantage on next attack). It's not so much that I think it's broken, just odd and showing slight favoritism when it's supposed to be about equalizing. I also think the doc is over complicating things by explaining every detail (when it can be left up to flavour) and adding extra attacks or replicating items that would be entirely possible anyway (eg. no need for normal weapon attacks or caltrops when a player can still do them normally).
Instead of making an awkward list of any modifications, I simply implemented my own simplified version and included it in my homebrew collection. Here it is.
The wheelchair can, and probably should, be upgraded to compete with the dangers that adventurers usually face. Some of these upgrades will simply mitigate the drawbacks, others are more powerful. It is always worth noting that other magic items are still as viable as they have always been. For example, winged boots will still work for a character in a wheelchair.
A wheelchair with All-terrain Wheels and a Hoverstone (80gp total) is basically the same (mechanics-wise) as a 30ft walking character (except for the option to double speed downhill). As such, I would probably expect those to come almost as default when the chair is built or purchased. However, a player does also have the option to take on more upgrades and even sacrifice the benefits of those upgrades for other upgrades. For example, if they don't expect to leave a city with mostly paved roads, they might forgo All-terrain Wheels in favour of Racing Wheels.
Prices are always variable and may change in game based on circumstances (and DM).