That looks nice! Along with scaling filters and line4x/5x, this should be exciting news to SNES owners.
Does apply_reverse_lpf have any effect on timing, i.e. does pclk3x Fmax still stay around 150MHz? Effective linetriple pixel clock is only 80MHz, but ideal Line5x implementation (not using HDMI_TX pixel replication as is done now) would need to run at at 160MHz in which case apply_reverse_lpf might need to be pipelined.