I would highly doubt that any saves would transfer. The way Early Access works is that new mechanics and items are always being brought in. Part of the development process means that things will change. And when things change, I'm sure Frontier will have to tweak certain things to get everything working harmoniously. The result of this? Incompatibility with older versions of the game. Think of another Early Access game, Prison Architect, for example; every month when they released a new Alpha 99% of the time at the start saves would not transfer. It's only when the game really started to fully flesh out did it get more consistent.
As much as I'd love to someday look back on my first ever Planet Coaster park, I just sincerely doubt that would be possible. Not that it's a bad thing at all though, I'd rather have better mechanics and a stable game than experience a tiiny bit of nostalgia.
You know what I mean?