A data transaction on the Tangle (a.k.a. zero value transaction) does not need confirmation. The reason for value transactions to all use a similar tip selection algorithm is that it increases the chance of getting your value transaction confirmed. However, a data transaction does not need confirmation and thus it doesn't matter which tip selection method it uses. It could for example just add the transaction to the two latest valid incoming transactions. Now my question is: in the white paper it is assumed that the majority of all transactions uses a similar tip selection strategy, like MCMC. This makes sense for value transactions, but we all know that the vast majority of all transactions are data transactions (like 90% or so). So now we end up in a situation where not all transactions use a similar tip selection strategy which has great implications for the convergence of the Tangle.
How can we still be confident that the Tangle converges?
We could very well end up with a (still consistent) Tangle that has a lot of different branches. This has implications for the confirmation time, and also for the formulas stated in the white paper because they assume a similar tip selection algorithm.