A few observations from what the implications seem to be from your post, please correct me if this is not the case.
Money seems to be getting tight, the game was scheduled for some kind of steam release nearly a year ago, however it has not reached a workable state yet. Development funds surely must be worn tight with being a year ahead of the funding schedule, so at this point some kind of path has to be made to secure funds for continued development. Early Access or look for a publisher.
From the time-frame you mentioned in Early access, the game would need at least 8 months of frantic development to reach a workable state from this point.
Clearly there have been early errors in the original calculations of how long this game would take to make which were put forward when calculating how much this game would need to be finalised. You guys put forward this to backers on kickstarter. While there are always unforeseen delays, the buck has to stop somewhere and at least some blame for it getting to this point is on you guys. I'm saying this to put it into perspective that the decision to get help from a publisher is something none of your backers agreed to when they put their money into the game your making.
Many Kickstarter projects of games die long before they reach the stage of Xenonauts 2, where Early Access is a feasible option. It is my opinion that if you have to take some negative feedback and work faster to ensure the game finishes in a workable state, then that is the decision that is closer in line with the agreement you made with the people who gave you money in the first place to create this game. Yes its not ideal and the game will have less polish, but I know I at least will look back on this decision if Xenonauts 3 ever goes onto kickstarter and remember how they could not make an accurate timeline of development and funds and then allowed unknown people into their project to make up the difference.
I hope you guys make the right decision, I put money into this game, I sincerely hope publishers that I avoid for their practices don't end up involved in this.