This is what Eugen Rochko the creator of Mastodon just wrote on his blog:

What to know about Threads

[...]

Our stance

We have been advocating for interoperability between platforms for years. The biggest hurdle to users switching platforms when those platforms become exploitative is the lock-in of the social graph, the fact that switching platforms means abandoning everyone you know and who knows you. The fact that large platforms are adopting ActivityPub is not only validation of the movement towards decentralized social media, but a path forward for people locked into these platforms to switch to better providers. Which in turn, puts pressure on such platforms to provide better, less exploitative services. This is a clear victory for our cause, hopefully one of many to come.

I actually think even if they kept it two way, most people will still use Threads. It's all about ease of use and where everyone will congregate. Don't underestimate the power of technical illiteracy or general don't give a damn.