I love Martha Jones - her character is one of the best and least appreciated, in my opinion - but I'm dreading if it's true that she'll be back for the spin-off. Because:
1) I hate RTD's writing and general direction right now because it's so bitter and smarmy.
2) Also, the plots are rubbish, and characters lack agency and/or likability.
3) There's been a whole lot of returning companions recently, and I think they need to stop propping up their show on known faces. That was one of the biggest lures of the soft-reboot with Tennant and Tate back. Once in a while, it's good and effective, but they should give it a rest for a bit, or it'll just get boring and incredibly obvious as fan-bait.
4) If they do a whole disillusioned, depressed hermit who is hiding from their past sins shtick with Dr Martha Jones, Woman Who Walked the Goddamned Earth, I swear to G*d... I want Martha living in the countryside as a country doctor with a happy family and a positive cottage core life post-UNIT retirement but gets dragged into alien hijinks in a series of bizarre incidents.
5) I think UNIT needs to be rethought a bit because it's been looking like a discount S.H.I.E.L.D, which is dull, uninteresting, and done. Also, we've seen a lot of them recently, and their appearances have been lacklustre and inconsistent. Especially Kate Stewart, who I adore, but I feel has been just kind of there for a while.
6) This one is slightly controversial, and since I'm white, I'm ready to be told otherwise, but I find it a little alarming how much people are like: "OMG Martha and 15! He's going to FINALLY apologise for 10's racism and they'll understand each other so much!" Firstly, in universe, the Doctor is an alien, and his understanding of human cultures comes from observation and visiting. He was never raised with any racial stigma, any bias or prejudice, and has always held themselves as separate and above humans. So how would him being (again, in universe) black help him understand Martha's life experience. To him, it would be like hair colour except for any passing racism he faces, which he has no qualms dismissing as petty small mindedness from 'lesser' beings. Secondly, Martha does deserve an apology for the treatment she faced (from the Doctor and the bloody writers) but not one that is almost glazed over because the Doctor has experience now as a woman and a POC. The Doctor, as a widely travelled and highly educated person who has seen suffering through the universe, had to have known that was wrong before that, and Martha should get an apology that isn't full of "that white cis man past version of me just didn't get it." Accountability and sincerity are important components to an apology, and I don't know if RTD can write that from his recent, hollow efforts.