1 - I think an option when you "Attempt to open coffin" will ask for payment. You simply pay the value whenever you choose to open it with the coins in your inventory - whether its when you go to the grave initially or at a bank. The mechanics of the actual opening would be interesting. I would initially say everything auto goes into your inventory and any extra falls to the ground. I wonder if it can be coded to where the highest "value" items auto go in your inventory or not. That would be something Jagex I think would handle. I would not like the idea of having stuff go into the bank automatically but that is a possibility with this. This idea could be tweaked a fair amount in different ways.
Well, like everyone else here, I strongly agree with the second idea, but not so much with the first. I think that the coffin idea is great, with the exception of a few things. First off - who do you pay to unlock your coffin for you? Secondly, what about non-tradeable items you lost when you died. They don't have a set "value" so, if all you lost was boots of lightness, and a dragon defender, how much would it cost then?
2 - I would actually expect them to not add to the price. Dragon defender doesnt have an alch value if I understand correctly and boots of lightness have a 3gp one so the effect would be minimal. I would say that they should not be given a set value in adding to the coffin or if they do add it equals their alch value. To put a "price" on these items would just seem weird/wrong to me. Items like Task items would still be lost just like they are in death now.
I have been told by many that the %'s for these ideas are far too high and that even a 1-2% on the GE and a 5% on death would be a great deal more understandable. If the %'s were that low would that make a difference with the idea for the GE and Coffin?