ritard feature requested

[ktnwin2012]

I also suspect it's technically complicated to alter the "clock".

Developing software is my life career. It is not that complicated to slow down a song.

There is a clock ticks in any computer based device (tablets, cell phones, PC, laptops, even digital watches).
For example, is the built in clock is 10MHz (10,000,000 ticks per seconds)
And based on the tempo (100 BPM), each beat has the duration of 10,000,000 / 100 = 100,000 ticks if the tempo is steady.

If we want to add a ritard from 100 BPM down to 60 BPM over 8 beats (2 measures in 4/4 time)
The "apps" can makes the computation as shown in the table below:
Starting from 100 BPM slowing down by 5 BPM per beat to reach 60 BPM in 8 beats:

beat# BPM #ticks
..1......100.....100,000
..2.......95.....105,263
..3.......90.....111,111
..4.......85.....117,647
..5.......80.....125,000
..6.......75.....133,333
..7.......70.....142,857
..8.......65.....153,846
last......60.....166,666
(sorry, I have to use the dots to keep the table above in proper spacing)

So, the apps only needs to increase the number of ticks in a beat and NOT really alter any clock (a hardware timer in the device).
Any software programmer can do this.
And all these are done when the apps generate the song, not during actual play time.