I am sure we will see the 55x again in the future. I dont think they will drop a mechanic that has already been introduced.
Depending how much money it made for them will most likely dictate how often they do the 55x.

Now on a personal level I feel like it was because the 6* featured was relatively meh (not 2nd pumpkin level of meh, but still meh), and thats why they tried that.
Coz - and I am sure of this - if they did this for Wallnut just two weeks prior, dude.... everyone and their mother would run with Wallnut in their party. I sure as hell would !

For now I will keep sitting on my gems. Need to replenish the pile, and will hope to see a 55x that actually is of relevance for me. Some nice Crit girl (though honestly they´d be hard pressed to do anything better than Wallnut. Loquat, Wallnut and Wolfberry are pretty much the crit girl MVPs, but I can see them doing some nice 1st turn crit chan.) would be nice.