The entire process is gonna take a really long time. The 25 episode anime covers the first 3 arc of the light novels. The author has written 6 arcs so far, and overall the story will have probably 12 arcs.
But also there's the chance that the series doesn't get picked up for a 3rd or 4th season. And light novels aren't really translated very well of at all. So the story could possibly go unfinished for non Japanese people
I forgot that we'd have to do it all again even in the best case scenario of a season 2 being ready within the next two years.
I imagine that the odds of second seasons that happen that much time after the first ones doing well is pretty slim, so yeah; season 3 much less 4 is probably a pipe dream.
This season was pretty much just a really well-done promotion for the light novel then, wasn't it?
I know most anime is, but series like this and
No Game No Life just hurt more than usual because they're so interesting and the source material isn't even done yet.