Does Monero have any plans of trading more on other platforms besides Poloniex?
Monero trades on cryptsy, bittrex, bter, and probably others I'm forgetting. It can also be exchanged via shapeshift and xmr.to (the latter, one direction). Where people choose to do business is up to them. I guess the exchanges that provide the best service will get the most business.
As a project we are neutral, and we help anyone who wants to support Monero. I've personally helped bter with their Monero stuff and cryptsy and shapeshift have also been on irc getting help from core team members and other knowledgable developers and community members.
So you are neutral about Poloniex having an separate XMR market?
Personally I really don't care what markets they have. I'm happy to let market participants work out what they want to do. That is just my opinion. (Not that they need my approval anyway.)
I'm not aware of the core team or any of the other core team members taking any action or expressing any opinions about it being particularly important.
We generally support whatever anyone wants to do with Monero, as long as it doesn't appear harmful.
Do you foresee "actively" trading on the other exchanges XMR is registered at?
Me personally? I've used some of the other exchanges on occasion, but I don't trade XMR actively, or trade anything actively at the moment.