The removal of discriminators will be terrible

Doing this will create name scarcity, paint targets of harassment and scammers on people who either have a high profile name or getting stalked, and overall limit your userbase's form of self-expression. This will also remove the incentive for your nitro subscribers to continue support, as they may have specifically paid for custom #'s. You risk losing a lot of your loyal customer base that had no issues with the current name system in favor of trying to make this app seem more "approachable" to new users, against everyone's benefit.  The current users have likely all been using very common names BECAUSE of the discriminators, so now they're forced to use names they don't want.

Let's weigh the pros and cons.
Pros:
- Forced latin alphanumeric characters will make it easier for servers to moderate
- You'll be able to make money from selling high demand usernames?
Cons:
- Messing up bots
- Typing someone's name to ping in a large server will be more tedious if they share display names with other people
- Forced name changes
- Unfair priority name changes 
- Unnecessary burden of protecting a high demand username account from hacking, scams, harassment, and even violence
- Removal of a widely beloved Nitro perk
- More incentive to create longer strings of names or more jumbled names because all the pre-existing "John" accounts will likely try to stay as "John" in some variant, with more new "Johns" coming in.
Instead of allowing 9999 different John's with an easy to hide, four-digit number, you'll now be getting a bunch of J0hn's and John123123's and xXJohnXx's, etc.

There's more reasons I haven't covered, but I hope this paints the picture enough to get the point across. The big takeaway is that they are trying to fix an issue that doesn't exist with a solution that will make things worse.