as Far as I've seen, You are never put in a position where your save is inaccessible and ***HAVE*** to restart
You are ENCOURAGED to restart, It may also be that your save is basically broken if you don't
But you are not REQUIRED to do so.

Examples being the updates between 0.0.9c - the coin thing. - the currency was changed from all in one unit, to multiple units in one of the versions - Having had MILLIONS in the one unit, different than all the other new units, meant even if it "filtered" because it exceeds 1000 of that unit, It didn't really know what unit to go to from there.
There was a save fixer introduced by Slipcor that sold off all ingots items and parts to allow the player to recover from that. - Making it so you could believably continue playing your same save.

In a previous update (ver 7 to ver 8 I think) The crystals were changed.
In the one version, You couldn't permanently keep them move, they would always Unload from the engine when you shut the game down, because they were not physically saved in your save, and scripted to reload with the game engine
They spawned with the game engine.

When the next version came that introduced code to allow them to be saved.
and you reloaded an old save
An old save that didn't have the crystals saved physically anywhere in your save and they were no longer scripted to reload with the game engine
That Meant that NONE OF THE CRYSTALS spawned in your save anymore. - Because they weren't saved when you reloaded, and didn't exist when you saved, and didn't reload with the engine or upon not existing.
Of course. This is less of a problem now. cause if they don't exist, there's a backup code that respawns them.
There's also a new save fixer by Slipcor that resets the crystals positions. - allowing you to recover them if they got lost or throw into the air

The updates inbetween each of those, hotfixes or larger patches that introduced content chance or additions, Like for example, The addition of Alloys (started off not completely configured) and then the change to alloys (could sell them and they had proper configuration for the most part) - didn't cause any interruption for old saves or new saves.

You could start playing, right now, and in the next update, Keep playing,
Though, From what I've seen of the next update. There will likely be changes and additions in Content, that will heavily impact an old save, in ways that may be hard to recover from. ***It's definitely recommended and heavily encouraged that you restart*** But I doubt the game will force you to directly.

And what's more important.

Is that Playing now isn't pointless.

You can't make real valid suggestions or critique the game if you don't play it and know what you're talking about.
You can if you do, you can see the direction its going, and know whether it may or may not be worth waiting for or supporting in its release.
You also can't remark that a feature was better before it was changed if you've never seen the feature before hand. - You can if you have.