[MonsterCross]

Is something like lanczos/spline/catmull-rom possible or are they completely different algorithms?

I think for catmull-rom you want something like:

Code:

vcgencmd scaling_kernel    0 -4 -8 -14 -18,-19,-16 -8  9 39 77 122 166 206 237 255
255 237 206 166 122  77  39   9  -8 -16 -19 -18 -14  -8  -4   0

But it's probably got too much overshoot. These kernels are operating on the [4:2:0] output of the codecs, which is encoded with gamma. So the effect is exaggerated in linear light on the monitor.
Kernels with nice mathematical or signal-processing properties don't always look best.