The UK has 646 Members of Parliament for around a population of around 60 million. My MP represents something like 100,000 people. (Can't be faffed to look it up exactly) So there is room for some expansion over the number of Representatives that you have. The Chamber in which our MP's meet and debate is also deliberately made too small for the numbers. On most occasions, the Chamber is not very full. On important occasions it is packed to the rafters.
A lot of the work of democratic representatives is spent in smaller committees and in researching and responding to their electors (or at least it should be) as much as it in debate and voting on bills.
So I would think there is room for some expansion but the higher figures mentioned remove any chance of human interaction. What would happen is that inner cabals would conduct the real business and would find a way of buying the votes of the lesser representatives. Much like everywhere at present I suppose but likely enough to quench any enthusiasm for such a drastic change.
There are better ways for smaller parties to find a voice but the stumbling block is always the parties in power. The only way is for the smaller parties to gain enough votes to get power in the traditional way.
And then of course they will be equally as unwilling to dilute their power.