I think it's a really great idea for you to "diversify" your blog post network through different TLDs.
As you probably already know, if you're building a PBN, you need to make it look as natural as possible.
If they're all .com, that may be a red flag.
Of course, it's not as intense or as ruby red or a red flag as the same class C IP block, but it's up there.
You want to throw off Google as much as you can so don't just stop at different IPs, different domain registrars, different hosts, as well as different themes.
TLDs can also go a long way in adding some much-needed "diversity" in your PBN network.