This is definitely not linear, and keep it mind it's only with a small amount of early adopter that they reached 125 Go mark.
As a matter of comparaison the whole database of the earth map at openstreetmap.org is as of writing only 36 Go fat when delivered in compressed form. https://planet.openstreetmap.org/pbf/
It seems absolutely ridiculous and a waste of ressource to expect that the blockchain shall never/ever use some rotating process to loose weight at some point.
Blockchain like technology can be very usefull, but current implementation look like a very rotten seed. And if a newer version that solve those issue emerge why on earth would they want to give any value to a prototype currency driven by opportunistics "first in" miners?
I desperately hope that no public fund was stupid enough to invest any real life saving to this mess because IMHO it's not a matter of if, but a matter of when it will collapse.
Now to be more accurate it might rather be a growth according to a logistic curve. Right now Bitcoin is used only by early adopters, but should Bitcoin usage diffuse among general customers it will growth quasi exponentially before plateauing.
A hundred years from now, you could store the blockchain on current day hardware. And that is without talking about improvements in technology.