I am pro-fediverse, so I guess making Mastodon atleast as easy to use as Threads is a must.
If you look at statistics, Mastodon always gains a massive amount of users, when Twitter does something stupid. Most of these also return back to Twitter, the moment they realize, that Mastodon has no VIPs.
If Threads integrates well with ActivityPub, then people on Mastodon will be more likely to stay, because Threads gives fediverse users access to the VIPs, that they used Twitter for in the first place. This stops people from leaving Mastodon in the short term.
In the long term Mastodon needs to advertise itself to younger people, because nowadays this is the only way for new social media platforms to establish themselves.
That’s how TikTok, SnapChat and Instagram became popular. This would make Mastodon fresh, while Twitter would transform into a graveyard like facebook.
Also having more tech companies, media orgs, cultural orgs, universities and maybe even governments host their instances, would make the federated aspect stronger and the whole fediverse more scalable.