I don't think it really means anything for any of our players except that there is now 1 more option for rotation, and cover in case of injuries.
There are some possible formational changes, but I expect our basic philosophy of using the fullbacks to attack, with the midfield being primarily defenders to stay pretty much the same, regardless of 433 or 4231 basic shape.
Remember Rafa saying "in this system, the fullbacks are the wingers" about his 4231.
It's the same now, just done slightly differently (although I'm sure that given the resources, Rafa's team would have progressed to a similar level).
It's all about options.
Anyone who thinks Thiago is here to "oust" or "replace" any other player is barking up the wrong tree.
He will complement our existing squad, and hopefully add a little in some areas.
In short, don't expect to see too much change.