The big issue wrt Turkey is not whether ISIL drop a few rounds on the wrong side of the border or whether they rampage through Kobane. In all likelihood, none of that will really get the Turks too worried. As far as they are concerned, the Kurdish problem is their main worry and the PKK are designated as a terrorist organisation, with the YPG, the main Kurdish faction getting clobbered in Kobane viewed by Ankara as an off shoot of the PKK.
There are only 2 things that might get them involved now:
1. Negative press in the international community for allowing the Kurds to fight on themselves without help - and even then, given their view of the Kurds this isn't guaranteed.
2. However, any attempt by ISIL to capture or destroy the Tomb of Sulyman Shah, which is a Turkish national monument and sovereign territory 20km inside Syria, and is considered near as you can get to sacred ground for the Turkish nation will result in Ankara getting very very very upset. So much so, that if you believe the press, they swapped out the ceremonial guard force with an SF detachment.
As much as it offends many western and humanitarian sensitivities, that Tomb, a symbol of Turkish history, is what you need to worry about wrt Turkey getting involved.