Well napoli there will be input lag, but thats the case even with ps4 and xbox one or anything you use on a new tv. You can set your tv to game or pc mode and turn of all postprocessing effects(noise reduction edge enhance etc) and greatly reduce the lag.
I play on a tv and while there is slight input lag its nothing gamebreaking or horrible. Ive beaten 100’s of difficult games playing them this way. I only noticed a real difference when hooking my pi up to a crt.