Q. Can I wait for Honda city BS6 diesel or purchase BS4?

If you are willing to wait for the BS6, you may be able to get your hands on the 2020 Honda City, which will be a much better thing to wait for than BS6, since the latter has little or no impact from a users perspective. This version will automatically be a BS6. So you win both ways, but the price differential may be approximately a lakh in my view, if you consider the year end discounts on the current model.

Should wait for the bs6 as its launching soon and has cosmetic changes also.

Go and buy BS4.. quickly. BS6 is of no benefit to you

You can purchase now this also perfect