Hi Robert,
at the last DKOM Björn Görke and Carsten Thoma showed some slides which nicely explained the relationship between HCP and YaaS. One of the slides had the title HCP is the best PAAS for YAAS. Which is a simplification but it quite nicely described that one larger part of the HCP is the Platform As A Service potion which will offer Cloudfoundry capabilities to customers. YaaS on the other hand is focusing on delivering a business platform to commercialize packages of microservices & UIs over a low-touch marketplace the YaaS Market and is build on top of Cloudfoundry.
So neither one is replacing the other. You can get a good overview of YaaS on the Devportal (https://devportal.yaas.io) and see what YaaS is offering to you in order to simplify the creation of your own packages etc.
If you have any other questions, please let me know.
Best,
Andreas