Its understandable that you do not want to releas game now, thats actually sign of good menagment from your side (releasing product, that you know is not soo good in curent state is a bad thing). Hoever people start to get impatient and alitle bit frustrated, which is understandable. I pesonaly will get really angry and most probably ask for my money back, if i do not get early acess to the end of this year, becouse there is huge amount of games that are ready and good. It was my choice to trust you with money and buy product thats not even ready on asumption that i will have a taste of it.
Well here is some things that in my opinion will make situation beter that you may try to do.
Some kind of battlearena like space battle in empire at war, for evryone that suported you.
Some kind of develop-meater that shows exacly what you want to do and how far you are - in the progress towards early acess, that wuld be visible for anyone.
Interactive ship modeling and some other tuches from the game on the side for example app that wuld show how reserch, ship design or other things, work.
There is also ability to give acess to infiltrator for those who are waiting for steam relese in time when you will be unable to go for some reasons on early acess and people still have no game that they payed for.
Gj and luck with development, those effects that you shoved on latest post (sun) looked great.