All of the State Street subway platforms have the length to accommodate 10-car trains. I have posted those lengths previously. CTA has published plan for future Red line alignment with a diagonal station marked "Irving Park". I am sure that station will have 10-car capacity. 35th St also will easily handle 10-car trains. The rest of the stations can easily be extended. The last time that CTA extended platforms was in the 50s...From Howard through Loomis/Jackson Park to accommodate the 6000 series PCC cars with their quarter-point side doors on the North-South route.