Four pillars is finished, fragmenting right now. A narrow bank is set to be rescued from the sewers of a Big Four controller. Others may follow.The disruption may be lame or lively, but the familiar model of an oligopoly of four - ANZ, CBA, NAB and Westpac - is being undone.The voluntary dismembering of the status quo by the cartel is rolling by in a manner helpful to long term interests of finance, banking and the shenanigans of profit reporting for the years ahead.There are champagne options in some eyes, the whole thing a nuisance to many. Our take? Rotten branding being split two ways.The following is a hypothesis centred on Sunday's news on ATM fee fiddles and drawing on our long running study of banking.A demerger option is bumbling along at Commonwealth Bank of Australia. Bankwest may be (or must be) the brand of choice to carry a slice of CBA footings into a world of independence and an early IPO.Bankwest - outrageously, in many eyes - is not part of the flurry of copycat ATM pricing cuts kicked off by oligopoly leader CBA yesterday (Sunday).One inference is that tactical options on pricing are being left to possible future custodians of Bankwest. NAB, which adopted a restrained version of the ATM fee fix, holds similar options.Drastic options are now on the boardroom table at CBA. A good bank/ bad bank split of some form or other must be one warm proposal still before chair Catherine Livingston and CEO Ian Narev.So where do the Bankwest brand and the Bankwest board and crew feature in thinking on local banking?Bankwest could be framed as "the good bank" in the bad bank wreck that is CBA.What claim would this separate CBA bank have on the moneybox, elephant and Which bank branding? Will Bankwest be THE bank with reach and respect and thus bid for the remainders of any CBA cult following on the share register? If the M&A moves unfold as we suspect, the politics of the carve up of market share will become clear. Whether those moves happen soon, are being considered or are right off the table, CBA may explain.The combined market share of CBA and Bankwest today is 27.03 per cent.This is less than the market share of the pair at the end of 2008. Bankwest then bought 3.37 per cent of the national mortgage book to the merger. It was 3.42 per cent when a crashing WA totem rushed into the safelands of CBA.Deposit market share at Bankwest has a rollercoaster feel. It was 2.95 per cent when household savings data vanished from the monthly APRA series at the end of 2012.Bankwest was a business fast losing market share when CBA fixers moved in. At the merger date at the end of 2008 the Bankwest share was 3.49 per cent, down from 3.71 per cent at the time of merger talks and the early 2007 peak for the HBOS owned entity of 4.01 per cent. A loss of 106