Plumtree has been with the Sharks since 2006 and took them to the knockout stages last season.
Crowley coached Canada at the last World Cup and Kirwan was in charge of Japan.
Despite large numbers of players to choose from within their boundaries, the Blues have struggled since their last title win in 2003.
Their results since have been fifth, seventh (under Peter Sloane), eighth, fourth and sixth (under David Nucifora) and sixth, ninth, fourth and this poor season with Lam.
With the final game left, the Blues have won three matches and lost 12 this campaign.
Despite that poor outcome, there is a faction pushing to reinvest in Lam for 2013, to use him on a coaching panel and tap into his franchise experience.
Others want a clean slate in the coaching crew, if not a broader administrative sweep.
They argue that results, poor performances and a dwindling fan base call for a total coaching change.
New Zealand Rugby Union chief executive Steve Tew said recently that his organisation wanted to undertake a wider review of the Blues and problems in the greater Auckland area which have beset the region for some time.
"I don't want in any way to shy away from the fact that we have challenges for rugby in that broader metropolitan area, but we are no different from anyone else in this country.
"If you don't get Auckland right then you have some real issues."
A group believed to involve Blues chief executive Andy Dalton, chairman Gary Whetton, NZRU reps Graham Mourie and Don Tricker and former All Black coach Graham Henry will evaluate those shortlisted for the Blues job.
Meanwhile a number of players involved in the Blues squad this season, which has expanded to 40 because of injuries, are waiting for the coaching decision before they decide on their allegiance next year.
About 10 of the original 30 players are heading overseas anyway, and another similar-sized group is struggling to convince they are Super 15 quality.
Some players have been contracted for next season but whoever is picked to coach the Blues next year will want to stamp their own selection mark on the squad.
Previously the Blues have said they want to announce the coaching decision by the end of this month.
Highlanders coach Jamie Joseph has signed with the Dunedin-based Super 15 side for another two years.
The 42-year-old former All Black loose forward joined the Highlanders in 2010 after coaching the New Zealand Maori and Wellington province.
Under his guidance, the previously underperforming Highlanders made strong starts to both the 2011 and 2012 Super 15 seasons before fading from playoffs contention.
Their most recent loss to the Reds ended their hopes of making the playoffs this season.
"We've made some real progress over the last couple of seasons and I want to remain because I have my sights on a very clear goal, to take the Highlanders to a Super Rugby final," Joseph said.
