Anime/Fan Service: I should probably clarify this somewhat... I said "bias" for a reason and that's to distinguish between my preferences and Cobl policy. Quoting from http://www.uesp.net/wiki/Tes4Mod:Cobl/Policy: "...the primary goal of Cobl is to provide a common library of defined objects, where such common definitions enable other mods to work together more easily or where such common definitions substantially reduce the work load on modders."
There are reasons for putting cosmetics/races into Cobl:
* Expanded cosmetics (eyes and hair) are heavily used in the community. Almost all companion mods and races mods use expanded hair and eyes. And while there's variability, there's definitely a common core of heavily used resources.
* Companion mods (a popular class of mods) would benefit substantially from a single standard set of expanded eyes/hair/races.
* Pre-made savegames would benefit substantially froma standard cosmetics set.
* An expanded set of eyes in one esm can be adapted to different meshes through a fairly simple patch mod, thus greatly reducing eye mesh/texture conflicts.
* Standardized cosmetics allow location (house/village/etc.) modders to use a much greater variety of resources, thus producing more interesting npcs, with a good assurance that the end user won't have too hard a time making things work.
* Single download of what tend to be large resources (eyes, hair, races), thus reducing download size of anything else that wants to use them (since user already has them installed).
Now for particular considerations:
* Much of advantage of Cobl comes from shared cosmetics. As a
toolbox races are most important for adding variety. E.g. if I'm adding an NPC character to a quest mod, then one race of dark elves is not going to be that different from another. E.g. if I'm adding some dungeon dwelling dark elves, then they probably don't need to be (lore breach) drow. Dark elves will work fine.
* However... In truth, Cobl isn't just a toolbox. Most users see Cobl as an end mod in itself -- and the addition of races drives it further in that direction. I'm not sure
how far Cobl should go in that direction; perhaps a good rule is that Cobl should remain "visionless". If you play OOO, then it's both "different" and "more". There's more stuff, but the gameplay is also different. While with Cobl, there's just "more" stuff -- style remains the same as Oblivion.
* The size of
just a race entry (without resource or birthsigns) is trivial, and does not provide a significant performance hit. Having that would still leave a race present in Cobl -- in a way that could be optionaly expanded.
* Race variants (e.g. male/female and/or tatooed/non-tattooed) have several technical problems (e.g. notably race relations), however there are likely some standard things that might be done to help there. E.g. globals like cobPcIsKhajiit to flag that the PC is some variant of the Khajiit race. Or cobPcIsDaedra to indicate PC is a member of a daedric race.)
* Size: Download size is important -- especially for Cobl core.
* If there are strong differences in taste for features, then they should be optional.
* It should be easy to install/use.
So given that, and looking again at say the Lineage Elves:
* They're dark elves. So, not that different.
* They're not lore friendly. And they're anime/fan service, which is contrary to Oblivion's style.
* However, if there were truly a huge demand for them, I'd put them in (and make them optional

.
So, back to bias vs. Policy. In practice, Haama and I are the ones who integrate stuff into Cobl. Naturally, we both have way more stuff that we could do then we actually have time to do; hence as a practical matter, stuff that we like/care about tends to happen first.
However, that can largely be overridden by someone else volunteering and doing the work. (E.g. dewshine for cobl food additions; Tashira Ronin for 24 hour clock option; Shawn5150 for NPC diversity.) So that can remove most of the effect of bias. But there will still be policy considerations.
So main point: Even if I have a bias against something (thong armor!), that's not a definitive "No". If it fit Cobl's goals and policy (complicated for races!), and if someone else does most of the work, then it's got a pretty good chance of going in.