Compactness of linear accelerator is significant factor in achieving short construction times, low infrastructure and operation costs, and is considered as one of key parameters for the next accelerator generation. Operation of XFEL and other accelerators shows the possible limitations on present technologies related to the RF power operation inside the cryomodules. The next development steps could be either further increase of Q0 factor of the cavities or other cooling methods. In the present paper, modification of the superfluid helium bath cooling scheme is presented. This will allow increasing the RF power by factor two or more. Application of the sub-cooling scheme for SNS/ESS/CEBAF-types cryomodules is considered. In order to operate at higher RF power levels, improvements of cooling methods for a fundamental power coupler are also discussed.