Four ADIs idly strolling through the door might prove a bargain for Bendigo and Adelaide Bank, although any tie-ups will hardly be a merger of equals.Nevertheless, leaving aside the merger that created the bank in 2007, it's been years since either Bendigo or Adelaide Bank snared a merger with another deposit-taking entity, although the previous three decades saw Bendigo move up from a century old building society in the Victorian goldfields to become an ASX-listed bank through a series of acquisitions and takeovers.There have been smaller deals. Bendigo in late 2012 bought the A$240 million loan book and related assets of mortgage fund Southern Finance at a small discount but so far has not been linked to any other mortgage debenture firms, despite the troubled recent history of the sector.Speaking after Bendigo and Adelaide Bank's full year profit briefing on Monday, its managing director, Mike Hirst, explained that "a long while back, the credit unions identified that [given] the additional capital required, their lives will be different."They looked at a couple of things; a consolidated balance sheet for all of them to work under."They are now looking at other models, ones that use someone else's balance sheet and use them for distribution," he said."We've had discussions now on and off for ten years, I'd reckon."The reality is if something comes of that, it's probably market sensitive. If the time is right to talk to people about that, we'll talk to the market first."