Yet again, on this topic there is very little material on the net.
I only found this link where they are talking about market share cap limitations:
Besides anti-monopoly and competition laws, which limit market share from 60& to 40% in EU laws in relation to bundling or mergers, or abuse of monopoly position ,there is very little else. IN US there are very few applied laws, the only one I came across the the limitation on bank deposits, which should not be higher than 10%.
In my theory of the Sovereign Economic Model, I advocate extremely strong market share limitations, especially in the consumer markets in things like FMCG (processed foods, personal care products) set at 10%, and hypothetically and ideally, even down to 3-5%. Obviously, in many strategic sectors, state owned corporation would remain without any such limitations, as would other types of companies like cooperatives at national level.
Very low market share limitations on markets worth billions will allow easy access to many small companies, thus increase competition, choice, prices for the consumers. So instead of having a handful of companies share a big chunk of the market, there will be tens of companies.
I also believe that the very low market entry cost and the pressure of competition in a market will force the companies to rapidly diversify in related fields, both with vertical and horizontal diversification. Therefore the competition will expands to related markets, a bit like expanding foam used in DIY.
Probably one of the difficulties for lawmakers would be to define strict markets where a limitation is applicable, divesture obligations, eventual IP licensing to competitors, fines and other procedures for non-compliance. There should be also clauses for innovators and first market movers which could have higher limits or time based exemptions.
But having such a legal framework in place, would first of all inhibit companies to push further for market share and block mergers or acquisitions for greater market share.
In sovereign, developing countries restrictions of market share could also favour local companies, as large foreign companies could not gobble up the market with using their huge financial and political resources.