After having been off for a while, I decided to go on and start a new island for Agrarian 2; because of the time gone, I don't really remember too well if there was a source of infinite lava, but when others were mentioning using pumps in the nether, it got me wondering if it had been handled. As far as I can tell, the tesseract would be able to offer a perfect channel to a creative tank of lava, is that what was done?
usually the sirwilli tank is there, to prevent people from pumping the nether, since this causes lag. and mostly on packs where you cant produce lava. on agrarian skies just pump cobble into a crucible with a heat source under it to make lava.
People still use the pumps because of the lack of a sirwilli tank. Crucibles take time to melt it down and I guess they feel the pump is quicker.