The Alexander storyline already introduced the concept of countless timelines:

'Alexander dreamed all the realities imaginable - all the realities mathematically computable - and in the end, reached a single, logical conclusion. It would change nothing, and erase itself from existence.'

...

'There was but a single time Alexander was spurred into action - not to change history, but preserve it. The summoning of the colossus, and events that followed, had potentially disastrous consequence for our reality. Its fabric strained to accommodate an infinite number of potential futures separated by nary a thread.' (Dayan, Lv. 60 Judgement Day)

Not every outcome is possible or even equally probable. Nor do past splits really matter, as we know from the short story that Yoshi-p references in the interview:

'Though we shall remain forever on different pages of history ─ and different books, besides ─ I take comfort in knowing we strive for a future of the selfsame brightness.' (Biggs III, Tales from the Shadows: An Unpromised Tomorrow).

It's a bit like how a quantum mechanical description of the universe might work, except where every possible sequence of outcomes is recorded in parallel as its own 'timeline'. Which could be the case, but we'd have no way of knowing because they would perpetually diverge and not be able to interact.

From a storywriting perspective, it doesn't really change anything outside of showing you 'what if' cases and letting you understand the consequences of decisions. You're still primarily concerned with one timeline, namely, the one we exist in.