Well, with planets some "superscience" sort of travel will be necessary, unless every planet is going to be 100 km from each other.
They don't need any sort of "superscience" warp drive or FTL at all.
Right now our ships are slow. Really, really, really slow. High end sports cars actually drive faster than our spaceships go. The only reason they are slow is physics issues, to be more specific collision issues - it only calculates physics 60(iirc) times per second. So if you're moving 100m/s that's 1.6 meters per physics step. Small blocks are 0.5 meters, so if you hit a 1 small block thick wall at max speed with a properly designed small ship you can already warp through it right now (in theory, I have not tested it). Increasing the speed limit will make that much, much worse.
So all they have to do is add some sort of "travel mode" that when enabled, adds a large bounding box to the front of your ship and uncaps the speed. If anything hits, or ends up inside the bounding box it just disables travel mode and rapidly slows you down to the current speed cap. If they wanted to be real fancy, they could even make the size of the box adjust every physics step, based on your speed. Even if they capped the ultimate max speed at lightspeed, the bounding box would only have to extend ~5,000 km in front of you. That sounds huge, but if they clumped asteroids together in fields which were spaced far apart from each other so that space really was mostly empty space, then even traveling at lightspeed would not cause a big problem. Things like time dilation would have to be ignored but I think that's acceptable.
Then we could have an actual, real, to scale solar system to play in, as well as adding fun new engineering challenges... like maybe thruster/fuel pods for interplanetary travel, or even just making carriers have a practical purpose instead of being just for fun like they are right now. Spacing the gameworld out like that would also have a huge amount of upsides, it feels like such a waste that 99.9% of every game world is practically impossible to explore right now.
The only downside I can see is people would be able to "emergency brake" by unmerging a single armor block or maybe even just jumping out of the cockpit. They could disable merge blocks and stop people from exiting seats while in travel mode, but it could probably still be abused somehow.
But I don't know if they are even considering anything like that, or if they think 104.4 m/s is "good enough".
Fun facts: if I did my math right, with 100 m/s^2 acceleration, given the game's simplified physics you could hit lightspeed in ~12.5 days. Since our infinite worlds are not actually infinite, you couldn't reach that speed without running out of space though. If you were somehow able to instantly reach lightspeed, it would take you almost 2 hours to travel from one end of the gameworld to the other (about one hour to travel from the center to one edge) so the world would still be pretty big even if you made ships with massive acceleration.