It depends on the games you are currently playing and the ones you will be playing in the future, the settings you find acceptable and the CPU of your system.
AAA games tend to be very taxing, so the (near)future AAA games may not perform well at 1440p ultra on 4000 series with a previous gen CPU.
In short, non demanding games and (most) 4000 series GPUs is probably overkill, but demanding ones it will probably not be.
No it won't be overkill, it's hardly the case that all the 4000 cards will be targeted at 4k. Besides there's no such thing as 'overkill', if you buy too much it will simply last you longer.Will the 4000 series be overkill for 1440p? I am currently on a 1070.