I too have an issue not being able to sell decimal quantities. Yards of fabric for quilting stores.
I have an idea for a decimal quantity plugin and I wonder if it is possible. Instead of using a decimal quantity in the quantity box, why not a separate box for the decimal quantity as an option. Then you can update the "Price With Options" accordingly. I think my idea would work for selling by pounds, or square meters, or cubic inches, etc. Please see my mockup attached with the example of:
1 [Quantity] X $10/yard [Price] X 2.75 Yards [Enterable Option] = $27.50 [Price With Options]
In my case, I would prefer to use a template with the quantity field hidden so that the customer only had to enter the "Length Cut" in yards and the quantity would stay at the default of '1'. However, some sites might want to sell two bags of 1.5 pounds of nails so they would leave it in.
That said, I don't know how my idea would work for inventory. My clients do need their fabric tracked in decimal yardages. But my idea would work for PayPal because they would be selling a non-decimal quantity of 1 cut of fabric:
1 [Quantity] Fabric [Description] Black [Variant] 2.75 Yards [Option] $10.00 [Price/Yard] $27.50 [Total Product Price]