Thought about it
and if you decide to go that route take a look at the layout of later H40's, maybe '88 to '90. They've got the dedicated dinette but I don't know if it lowers down to convert.
Whenever I get around to fooling with ours (an '85) I'm going to reshape the table a bit and round the corners and trim the aft edge back a bit to make getting around it easier.
As far as making the berth into a double, I'm going to make a fold up leaf that will be hinged fore-and-aft along the lip of the settee. This would turn it into a very tight double or a palatial single. The biggest reason I'm going to do this though is that the table will make an effective "lee cloth." Having an easy-to-set-up sea-berth is far more important to us than having that 7th or 8th berth only used once in a blue moon.
Having said all this, whether or not your mod makes sense will depend on how you use your boat. I don't think we've ever spent the night with eight people on board. Whatever you do, be sure to take lots of pictures and share with us. Good luck!