As was implied by the surprise Czech return last year, we don't have a complete list of the countries who've applied for provisional participation. It still could go up; I'm pretty sure we have fewer definite "no"s than we did at this time last year.
Yeah, I'm being cautiously optimistic at the moment. There are certainly plenty of countries in doubt, but given that it seems we should have a return from Turkey and Ukraine, some small chances from a few others (Bulgaria/Croatia etc.), and there are no confirmed withdrawals from last year, I'm hoping that we'll see over 40 countries again next year.
Is this list of confirmed participants definitive? I mean last year Bulgaria also announced its participation, only to withdraw later.
It's not definitive yet, no. Generally there are one or two countries who put in a tentative submission only to withdraw it later (Bulgaria and Bosnia/Herzegovina last year). Those countries who withdraw tend to be the ones who are trying to return, rather than those who participated last year - a withdrawing country will generally just state that it's withdrawing, or not put in a submission at all. Case in point - neither Bulgaria nor Bosnia/Herzegovina, the late withdrawals from last year, had participated in 2014.