I don't think Alton Towers really has any need of any budget family/kids rides at this point. I also don't really want to see Alton Towers - and indeed the rest of the Merlin estate - become bargain basement shoppers, as Drayton and Co. have become - just leafing through the Zamperla catalogue - or even worse, SBF or cheaper. That isn't to say those manufacturers don't have their place - indeed, a small number of Zamperla's products are good, but a park like Alton needs to be aiming higher.
The gap in Alton Towers' market right now is twofold. The young family market has adequate provision for the next few years (although the marketing power of CBeebies brands will probably lead to additional rides in this area sometime before 2025). The older family market needs further work. Even with Walliams, the area is still going to lack and I hope to see a new waveswinger and returned use of the theatre before too long. Indeed, I believe that had GG opened on time last year, we could have actually seen development here this year. Beyond this older family market, the park's glaring issues remain a lack of flat rides: many have been lost in the last decade and not replaced. The ones that remain are old and should already have gone. Easily two are required moving forward - more to replace Blade and Enterprise. A multi-ride deal with Huss, Intamin or other wouldn't be a bad thing. The other major problem is the dead wood in the park: Nemesis Sub Terra and Dark Forest. NST needs either overhauling and using, or removing. Dark Forest needs a comprehensive retheme.
Sadly, the Smiler incident and now the C-19 pandemic has delayed hope for these areas to be immediately addressed, but I don't believe Alton Towers are naive enough to not appreciate this problems. It depends whether Merlin, now under Lego of course, are ready to cough up. I would like to think Merlin see how flat rides are far cheaper to install than a rollercoaster and, with Alton's marketing might, this could easily be a big advantage.
It's safe to say that Lego Group wouldn't tolerate bilge like Dark Forest or clapped out rides like Blade at at Legoland park.