If the House of Representatives had that many members, it would be a nightmare for each of the party's leaders just to manage and communicate with the members of their respective parties. The leaders would have to have their own lieutenants who in turn would have their own lieutenants and so on and so forth.
For example, Steve Scalise, who is the House Majority Whip, would have to delegate a huge chunk of his work to his subordinates in order to make sure that his fellow Republicans vote lockstep on a House bill.
I actually see the opposite -- since each House member represents a district so small there will be less incentive for the representative to "act-out" since the party at large can easily find a replacement. There will be a strong inducement for parties in federal elections to select candidates who tow the line.
But the threat of institutional gridlock is there in the sense that the House leadership will only present bills that have absolute assurance of being passed, which means bills of no particular significance.
