Is there a reason not to mention the readings τι ημιν και συ and τι εμοι και συ in the above mentioned verses in ECM Mark print and Online?

The INTF-collations have a total of 640 Verses with τι εμοι/ημιν και σοι/συ (Mt 8:29, Mk 1:24, 5:7, Lk 4:34, 8:28, John 2.4); 145 have συ instead of σοι, so over 20%.

Thanks for your note.

We do not take τι ημιν και συ as a variant, because the nominative συ is hardly understandable in the context and rather to be considered as itacism. The mixing of the vowels  οι and υ is widespread. Itacisms are regularized with an "r" after the witness, but you will only see witnesses in the edition when there are variants. 

I do understand the qualification as itakism, but when in almost all other instances of συ < σοι less than 4% of the mss. show this itakism, and in all cases with the expression τι εμοι/ημιν και σοι over 20% have συ instead of  σοι and there are even mss that only in these expresssions show συ < σοι, nowhere else, the probability, that this is not just a matter of itakism seems to be high.