That honey castile soap sounds luxurious!
Since lye is the fragrance killer, I wonder if adding botanicals to a MP base would work? Correct me if I'm wrong; there's no lye in a MP base right?
FALSE! Lye IS used in the manufacture of MP soap base - assuming it is SOAP and not some type of detergent. There is no lye present in correctly made soap of any type - CP, MP, etc - b/c it has been combined with the fatty acids and become a new substance - sodium lardate, sodium cocoate, sodium olivate, etc.
The scented substances you might add to cold process in place of water - such as rose water, milk, beer, wine, coffee, tea, etc - you would not add to MP. You could maybe add a small amount of them - a teaspoon or so per pound - but not enough to give scent. Another way people have tried is to infuse oils with something, such as rose petals, and then turn the infused oil into soap. You could infuse an entire pound of, say, olive oil, with rose petals and have it smell quite lovely, make soap with nothing but water, lye and that olive oil, and get no rose smell. Or you could try adding a small amount of that olive oil to some MP, for example, but again, you wouldn't have the scent concentration to make a different.