No issue in terms of location, or even having an added button for specific amount. Just having that as the only option takes away from flexibility already in the game that a large number of players use.
@Dhurrin You appear to be focusing mostly on kp chains, which is where I see the main benefit of a specific amount or confirmation coming into play. While I see plenty of fs, using that option I see a huge amount using forms of self-levelling where the issues in dropping KP aren't there. You also have direct swaps which can often accommodate large volumes of KP and wonder societies. Then there is net0 which is a type of self-levelling but also uses precision depending on which side of the donation curve they are on but there is options in that one to use runes and instants to minimise issues. Not even looking at other methods I can't think of or am not aware of.
From my personal observation self-levelling is the most popular method of levelling wonders and to increase clicks for a large portion of the player base I don't see as a good option unless there is a major issue to remedy that justifies that. While the devs won't have stats on who uses what method of kp levelling they will know how much kp someone puts in their wonder verses someone else.
Your not trying to convince me, you need to convince the devs (if such an idea can even get to them) that a large portion of players self levelling needs this feature. Otherwise you need a solution that doesn't detract from those players while meets your goals to even have a chance. To make that job harder my experience is a lot of self-levelers are newer players, so the devs target audience that they want to protect and cater to.