I've got a very strong feeling that LTCC filters are coming inevitably to the RF & microwave world. The manufacturers only need to get their processes right to achieve constant and small enough line widths and substrate thicknesses. The dielectric constant and losses of the usual materials are not a problem any more, but the variation of dimensions may still be.
And perhaps these things could also - one day - evolve to HTS filters, when they start using suitable conductor pastes for superconductive operation. This may take a few years, but I feel them coming sooner or later.
Hobbie