It's not set to start till September, which might actually be a little optimistic if they're pushing live experiences like escape rooms, given we might still be under lockdown then. We'll see though. If it is as broad as it sounds, it will likely be very expensive to buy all the different media and experiences for the story, but hopefully there'll be a solid core story that can be enjoyed without breaking the bank. It puts me in mind of the huge comicbook crossovers that Marvel and DC do from time to time, that require buying several issues from multiple titles to follow the overall story, and are almost inevitably disappointing. On the other hand, it's exciting to have various different ranges, which are usually quite separate, working together on a storyline. The last time there was a concerted effort for spin-off material to work together was probably in the mid-nineties when Doctor Who Magazine tied its comics directly to the New Adventures novel line. (It also means I'll probably end up re-subscribing to DWM after letting my sub end for the first time in almost twenty years.)
I'm very excited to see the Eighth, Ninth and Tenth Doctors involved in a story together, which is a combination we've never had before. It's very rare that 20th and 21st century Doctors meet in expanded media (Eight isn't exactly Classic Series and he's more 21st century than 20th but he did arrive in 1996 and his licensing is mostly tied up with the original run.) I expect we'll have audioplays featuring both McGann and Tennant, hopefully together, although I highly doubt that Eccleston will be involved in any way. It would be an amazing and welcome surprise if he was though, and having Nine facing Ten, even just in prose or comics, is something to look forward to.
Given the title, and the scary, beaten-up Tenth Doctor in Prydonian robes, I think it's safe to assume that this involves the Doctor at the end of The Waters of Mars, possibly going off on a tangential timeline rather than getting to grips with himself. The official Doctor Who site's story page even has a placeholder entry for it after Waters which is a unique step, so it's safe to say this ties into the Doctor's crazy dangerous turn in that episode. I imagine we'll see Eight and Nine confront Ten rather than simply working with him, although I'd put money on everything being reset at the end so it can proceed to The End of Time and the regeneration. And defending "the universe from a terrible race"... that's got to be the Time Lords, hasn't it?