Personally, no I don't think it is.
Different businesses have different business strategies and models - if they all ended up using the same infrastructure, you would just see entities selling very similar products and all to the same customers.
In addition, if all telco's brought shares, they would all want Openreach to do different things in terms of investment and/or where firms have their own infrastructure already, they may not want Openreach to invest in those areas - giving them a competitive advantage - and they are likely to be the bigger firms, so would be likely to have higher shareholdings..