Hidden Services are in a peculiar situation: they see a loyal fan-base, but there are no dedicated Tor developers to take care of them. This results in a big pile of features that need to be researched, implemented and deployed to make Hidden Services more secure and effective. The current Hidden Services architecture does not scale well. The long-term keypair of a Hidden Service is an RSA-1024 keypair which nowadays is considered weak. This means that in the future, Hidden Services will need to migrate to a different keysize and/or asymmetric cryptographic algorithm.”]
Source: https://blog.torproject.org/hidden-services-need-some-love