One of the biggest issues with this system would be that a rich company or individual could buy large blocks of votes on a particular issue.
Another might be that a delegate could present a popular set of views in public for the purposes of gaining a large number of delegate votes but then they could privately vote for their real beliefs which might be much more fringe, or perhaps they might change their mind close to the election.
AFAIK electoral college delegates are selected by secret ballot so they can't directly buy votes. A similar system could be adopted in theory, but you might want to know whether you are casting 1 vote or 1000. For example what happens if 10% of the vote is delegated to one person who doesn't turn out to vote?
Regarding 1, if you're directly attempting to intimidate/coerce/bribe enough people that it will make a difference, that's a lot of chances for something to go wrong.
Another might be that a delegate could present a popular set of views in public for the purposes of gaining a large number of delegate votes but then they could privately vote for their real beliefs which might be much more fringe, or perhaps they might change their mind close to the election.