Genitivesis Issue or the Genitivos Issue?

So, I had my Hittite 2 test today. It included Hittite, Hieroglyphic Luwian and Lycian. It went fine, but as I was busy working with it, I stumbled upon the last question of the test which went as follows: What can you tell about the genitive in Anatolian languages?

The answer was easy enough, and I'll give it as an introduction that is to come.

Anatolian languages seem to have two separate ways of creating a genitive construction. One is by the typical genitive ending suffixed to the possesor. This is Proto-Anatolian *-as (Hitt. -aš, Luw. -as, Lyc. -eh). This just goes back to the typical Indo-European genitive suffix *-ós (although some might argue it's the other way around).

What is interesting about the *-ós suffix though, is that it is also seen in the Anatolian a-stems (PIE o-stems), while in the later PIE languages we tend to find the pronominal *-eso, or even a *-esio (and maybe *-eio).

The other way of creating a genitive construction is the -ssi- suffix (Luw. -esi, Lyc. -ehi), oddly enough this formation seems to be absent in Hittite, while it is dominant in Hieroglyphic Luwian and Lycian, and the only formation in Cuneiform Luwian. This formation is typically Anatolian and works quite different from what you're used to.

I'll give an example of both the traditional genitive construction, and the Anatolian genitive.

Both forms can be found in a Lycian trilingual on the founding of Xanthos (a Lycian city). The *-as genitive is used as a so called onomastic genitive (a genitive used for names), while the *-ssi- genitive is used for nouns.

ẽke Trm̃isñ χssaϑrapazate Pigesere Katamlah tideimi 
'When Pigesere son of Katamla became Xadrape of Lycia....'
The Genitive construction here is Katamlah tideimi. where -ah goes back to *-as (though we would expect **-eh, but there's still many things we don't fully understand about the *a>e shift in Lycian.)

se-t-ahñtãi χñtawatehi χbidẽñnehi sey-ArKKazumahi
'and to be of the king of Kaunos, and of Arkesima'
And there we have, not one, not two, but three -ssi-genitives!
χñtawatehi, χbidẽñnehi, ArKKazumahi. What's interesting (though not particularly visible in this example), about the -ssi- suffix, is that it makes it a new noun, which afterwards, just conjugates like any normal noun. So *-ssi-s is the Nominative, *-ssi-n is the accusative, etc.

So here is approximately where I ended my answer, and, my answer had less cool examples and diachronic notes, but you get the point.

So, now that we have an overview of Anatolian genitives. Let's look at some other Indo-European languages.
First Greek:
Standard for all consonant stems is the -ος genitive. For example:
πατηρ > πατρος
o-stems though, work differently. they end in -ου. For example:
ἱππος > ἱππου
This ending could come from a variety of sources.
Some idea's are: *eso, *eo, *ejo but definitely not *esio. The first *e could also be an *o, and technically the final *o could be an *e if the first letter is an *o. *eo is dismissable if we're to assume it's from an Indo-European origin.

*eso is the most likely, since this is what we see in the pronouns, which in most cases seem to work the same as the o-stems.

Gothic has -is, which should be safely derrived from *eso as well.

But then comes Sanskrit to screw it all up!
Taking the same examples (etymologically) as Greek:
pitā > pituḥ पिता > पितुः
This formation is rather weird, I believe it points to a *-r-s ending, and thus proterodynamic rather than hysterodynamic as seen in Greek. It's not that relevent though, the word for horse (an a-stem (PIE *o-stem)) shows a very odd genitive:

aśvaḥ > aśvasya  अश्वः > अश्वस्य

An -asya suffix. This could be from a variety of sources, the likeliest ones are *esio or *osio. It might just be me, but I think the -sy- part looks an awful lot like the Anatolian *-ssi- suffix e-si-o. An *e thematic vowel, *-si- suffix, and an *-o ending. What exactly this *o-ending would be is unclear. Maybe it's an *-e, and then it would be an old vocative suffix. Maybe it's based on the pronominal ending *-eso which might have sounded enough like *-esi to start influencing each other.

When I presented this idea to a fellow student of mine, he pointed out the rather odd dative plural of consonant stems in Greek, which is made with a -σι(ν) suffix as well!

It's hard to explain how a genitive *-si- ended up in a dative plural. But the current explanation isn't too satisfying either. People generally compare it with the Sanskrit locative suffix -su सु/षु. But an ablaut of i/u isn't what we like to see in Indo-European.

So to conclude. There's two types of genitive constructions in Anatolian languages. The true genitive *-as and the genitival stem extension *-ssi-. There are some indications, especially in Sanskrit, that this suffix may have already existed in Indo-European itself, but only ended up being productive as a separate category in the Anatolian languages.

I am quite sure there's other Indo-European languages that have evidence for a -si- genitive like Sanskrit does, maybe Slavic languages? I'm not sure, but if you know, please leave a message.