You are correct in all you stated mate BUT It's all in the past and we are talking about now. Yes Kula has done really well but he is not scoring runs or taking wickets so I maintain he currently is a passenger- you will recall I also suggested thirri was dropped whilst in a England but you argued against it ..
Also Priyanjan has done far more than kula recently so no way he should make way IMHO..thisara will also feature in our World Cup plans as he is the only "hit the deck" bowler we have - which I think will be essential on hard wickets in OZ
Well just on the bolded, you might recall in the fifth ODI he played a matchwinning innings, so I think it was rather well worth keeping him in the side, and now he's starting to find some form (last 3 innings: 60no, 13, 36). I imagine he's probably grown as a player from the experience and he'll have the confidence that he has the backing of the selectors and that he can pull himself out of a slump at international level. (Now watch on as he throws it away in the 3rd ODI now that I've said this).
If you drop someone for going through a form slump every single time you won't get very far, you don't know how close the next good performance is and even when he isn't taking wickets as he showed in the first ODI he can usually keep things tight even when he doesn't take wickets, so I don't see the drastic need to drop him at all.
Given you appear to think Thisara should replace him, think about the team balance issues that creates, we are already playing with 7 batsmen, given that Thisara's stronger suit is his batting that almost means we really would only have 3 genuine bowlers and be relying on all-rounders and part-timers for 20 overs (possibly more) in every ODI we play, really not liking that idea, sounds ok on paper given the options we have but I don't think it would work so well in pressure situations. Given that Priyanjan effectively threw away his chances of batting higher than 7 after that wild slog I think the battle between him and Thisara is over the no 7 spot, generally a spot in the order that a big-hitter is required, on batting alone Thisara probably fits that role better, but than again Priyanjan's versatility is also handy if he lose a lot of wickets and need him to help re-build an innings.
And on the point of needing 'hit the deck' bowlers in Australia - check
this out... the stats appear to show that our two seamers that rely mainly on swing and accuracy (and changes of pace in Malinga's case) are the ones who've done well in Ausralia recently. Note Perera's high average and high economy rate, given that Matthews is already in the side and able to hit the deck quite hard I don't see the necessity for another bowler of this kind, and if we really wanted one I suspect someone like Dhammika Prasad could replace one of the spinners we have in the side currently, it's a bit of a long shot but Maharoof could also be an option given he has had some success in Australia on previous tours and is style.