Investment Management: No limits to Size?

Talk of (inevitable?) concentration in the Investment Management universe must lead to the obvious question: is it really inevitable as many consultants and industry bigwigs are saying or is there a natural limit to ever-expanding amount of aum among the industry giants such as Vanguard, Blackrock or JP Morgan?
There may well be the result of at best matching the investment benchmarks (minus fees, costs) as the sheer size of portfolios makes any meaningful divergence from the benchmark more and more impractical. So even active management will be not much different from passive management the bigger a provider becomes.
Product differentiation may provide a (temporary)?) solution as the myriad of strategies can again try to be nimble small fish in a big pond. So effectively big investment houses become a congregation of investment boutiques under the same roof - be they separate subsidiaries (as at Natixis for example) or just different teams under the same umbrella.
Which leads to the next conclusion: if boutiques are the way to at least try to make active investment management work who is to say that free-standing boutiques or even mid-sized firms are necessarily at a disadvantage? Everybody knows where the big pools or money are and digital distribution channels will keep the costs garnering assets under control.
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