Now, the sex part is fun. I hope that part doesn't go away for recreational purposes. ;)
The thing is....
I feel quite certain that within a century or so there will be no need whatsoever to have sex (or physical stimuation of any sort), in order to have the pleasure and excitment we associate with it. All we will need is a chemical or two (ecstacy comes close), and we will be able to stimulate our BRAINS to experience whatever we want, whenever we want. This is not really all that difficult.
Already women do not need an intimate encounter with a man to have a baby, and men most likely will be able to have children at some point in the future, and beyond that, if our species survives long enough having children as we do today will become obsolete.
Why would we think heaven is limited to this moment in our human development?
Think back to the time of Mitosis... the creatures of the day had no idea there could be a new way of reproducing. Meiosis developed as life found a better way to survive.
We are a very young species and sexual reproduction is relatively new to life... my guess, there will be much more to come!
If there is reproduction in heaven I feel quite certain it will be in a manner way beyond our imagination.
Just a guess... :-)
~dancer~