Any path into the mid/late game other than the player being expected to take initiative and engage in wholesale conquest seems to be a bit underdeveloped at this point. If the game sells well (by paradox standards it seems to be doing just that given steamspy) they'll flesh out most things via DLC, but for now anything but a warlike playstyle will probably lead to boredom further in.
There's fun to be had with Stellaris, but there's definitely issues for certain play-styles, especially given how these end game crisis events will force players to gear for war to a high degree no matter what if they want to stand a chance.