As far as I remember Siege Towers should be in the next row for all civs since bombard cannon has the houfnice upgrade.
There are two problems with changing the rows:-
It messes with the hotkeys which is linked with the grid layout of the unit/tech icons. So we cannot just change icon position for one civ randomly since it will make a different hotkey for only that one civ.
Units that need upgrade have to have a blank below them free but there are only 3 rows in total from top to bottom.
We have a different thread discussing this exact same thing. For the same reasons mentioned by others here, the civ will never get knights but they do need a rework of urumi, an alternative raiding option from barracks or something.
As for the topic, no Knight, Camel or SL or any new UU for them. Just replace one of their naval bonus and/or the siege discount bonus and/or Medical Corps UT to a Militia line bonus the will Eaglize their militia line.
For example Medical Corps changing into : Militia line +20% speed and +2 PA. Champion is removed.