Most movies are fixed in a tangeble medium months before week one. Sometimes years. Component parts (principle filming, scripts, original music, if any) are routinely finished at least a year before release. A rush to get everything out to enjoy the full 3 years of income potential would further push out the couple of films a year made where people actually cared to do things right.
20-30 years might be right, though. Or one of the escalating fees for renewal after a reasonable period, preferably with a required deposit of the work so when it becomes public domain it can be easily distributed.
1. You're only considering works published by huge multinational publishers with the gigantic marketing budgets required to get immediate traction
2. You assume that works are published on a large scale for their initial publishing
Small time artists can spend years trying to get a work picked up by large publisher. Those who don't choose to use large publishers may be finding new audiences over longer periods.
Assuming that copyright should be designed around the use-cases of Comcast or Disney is the reason we're in the position we're in now.
Sure, under the current system.
The question is how many people that would have bought the media would just wait out the copyright. Once you're into these short lengths of time, it's a lot.
When you're talking about timelines as short as weeks, you're going to get a ton of people waiting. They might still go to a theater, even, but one with much cheaper tickets.
How many at 3 years specifically? I'm not sure, but it's a risk to be considered.
Perhaps this would affect less known artists. I would be willing to keep the copyright until the first 100,000 or 1,000,0000 worth of product is sold.