Prior to Paul Hesters death in March 2005, there were strong indications that Neil Finn was to do a Crowded House reunion at the end of 2005. One of Pauls final performances, if not his last ever, was reuniting with Neil and Tim Finn in December 2004 to play a couple CH songs with them for Australian tv. After this occured, Neil indicated that he was interested in reuniting the band after his 2004-2005 Finn brothers tour ended.
It's hard to imagine Crowded House without Paul Hester, but Paul quit the band in early 1994 while on tour in the US and was replaced by Peter Jones. Peter technically was not an official member of the group but he did finish out the Together Alone tour with the band and went on to record with the band on their initial recordings for their 5th album, which was never released.
Mark Hart had toured with CH as their keyboard player for the Woodface tour of 1991-92 and became an official member of the band for their 4th album Together Alone. After Paul left the band, they were back to the trio of Neil, Nick and Mark. When in 1996 they chose to record 3 new songs for a best of album shortly before they broke up, Paul was brought back in to play drums on those songs, but was not considered a current member of the band. As the best of album was about to be released, Neil decided to end the band and when they did 2 farewell performances in November 1996, Paul came back to play with the band.
The Crowded House that is reuniting this year is their final official line-up: Neil Finn, Nick Seymour and Mark Hart. The upcoming CH album began as a Neil Finn solo album where Nick played bass throughout and it has morphed into a CH album. Mark does not appear on the album unless he was added to it with overdubs when Neil came to Los Angeles (where Mark lives) in December to finish the album.
It's completely accurate to call these 3 musicians playing together as Crowded House, as what we will be seeing is the final official lineup of the band.