I don't want to come across as an asshole but I am completely lost by some of the basic premises here.
1. How are pixitracker or nanoloop trackers?
2. Why do you think that trackers are good for touchscreens? They are based on text input and if you try any of the existing mobile trackers you will see that they can't compare with desktop or even gamepad trackers in terms of workflow.
3. Not sure how the likes of LGPT would work on touchscreen unless some serious UI changes are made. Even games with virtual gamepads mostly play like shit. Why not use LSDJ under a GB emu on your device to see how it fits? I find it quite troublesome when I need to hold 2 virtual buttons and press the third one.
Milkytracker is pretty much just a curiosity. I don't think it's usable at all, it's more like a player.
Sunvox is the only serious attempt at mobile tracker that I tried and it is usable, but lacks the ease of use that makes trackers stand out from pianolol-type apps in the first place. Otherwise it's very well implemented and feature rich.
Also there is sinusoid for iOS but I don't have an iOS device anymore so haven't tried. Anyone used it? Seems to be geared towards chipmusic specifically.
http://www.humbletune.com/sinusoid/
Also this thing is coming up but I'm not exactly holding my breath it will be usable at all:
http://www.vividtracker.com/