How much current HTML5 would remain as is?

Hello everyone****

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I have been asked the question as appears in the subject line by a web
design company who had been developing new sites using HTML5. In the light
of the likelihood that some elements/attributes of HTML5 would be modified
in the course of time, about how much modification on it would be
reasonably expected to be made which may impact sites recently developed
with HTML5? ****

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Any guess may be helpful.
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Thank you for your time reading this.

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Dai****