The X-languages are quite different from each other and do not form a unified family of any sort. They surely aren't cognate in the historical linguistic sense as, for example, Low Elvish and Macaronesian are cognate. None of the X-languages has a conculture attached, and none is intended to be naturalistic.
What I am not going to do is to propose any of the X-languages as an auxlang or anything like that. They are experimental and way too bizarre to be actually used (for example, I doubt that any human can parse an X-2 sentence which makes ample use of the language's stack-manipulation tricks in real time); and I am doing this (as all of my conlangs) just for fun .
I am also not going to say goodbye to naturalist artlanging. My main conlang project is still Albic. But there are some really crazy ideas in my head that fit neither there nor in any other naturalist language, and want to be let loose in experimental languages.
It is also very unlikely that any of these projects will ever reach a high level of development. My interest in these projects (and the knowledge that would be required to do them properly) is too limited to follow through on them.
List of X-languages
X-1 is an attempt at "Jeff Prothero's Plan B done right". It emerged from a discussion of Plan B with Raymond A. Brown on the CONLANG mailing list in 2005. The language is meant as a logical language which achieves self-segregation by indicating the length of a morpheme in its binary encoding: the length of the morpheme (in bit quartets) is the number of initial consecutive 1s +1. For instance, a morpheme beginning with 11101... would be 3+1=4 bit quartets long. The project soon lost momentum and is now dormant; I consider recycling parts of it in Loc, an interspecies auxiliary language in the Trellis universe.
X-2 was an attempt at a stack-based language which tried to avoid some perceived SAEisms of Fith in favour of a more formally streamlined syntax with only one class of content words. The phonology was meant not to use the lips (and thus be lip-reading-proof). The project was abandoned soon after its inception.
X-3, now named Quetch, is an attempt at designing a practical speedtalk. The language has not yet been worked out; the plan is to use a large phoneme inventory (ca. 120 consonants and ca. 20 vowels), and an inventory of morphemes that are one segment long. The language would be oligosynthetic, with content morphemes (and pronouns) consisting of single consonants, and grammatical connectives (such as case markers) consisting of single vowels. So far, only very small parts of the language have been worked out. The project is currently dormant.
X-4 was an attempt at a musical language which could also be spoken, by using the consonants b c d f g and the vowels a e which could be pronounced as such or interpreted as names of musical notes. The language was never worked out and is now abandoned.