You are right. IR also dont want anyone to shift from AC3 to AC3E. Gap between SL and 3AC is too large. if 3ACE fare is made affordable for SL class pax, then IR wont be able to reduce losses & there is risk of 3AC pax shifting to 3ACE if high fare gap is there. So 3AC & 3ACE fare difference is kept less. Affordable AC ke chakkar mein IR ko barbad krne ki zarurat nhi hai. Unreserved AC class is better idea.