"The global metrology community expects that a revision to the SI will be agreed in November 2018, when the General Conference on Weights and Measures meets...From May 2019, all the base units of the SI will be defined in terms of constants of nature...The kilogram is defined by taking the fixed numerical value of the Planck constant h to be 6.626 070 15 × 10-34 when expressed in the unit J s, which is equal to kg m2 s−1, where the metre and the second are defined in terms of c and ∆ν."

How much of a change is that likely to be? I can see it being importast for scientific studies, but not so much for fencing unless it's actually large.

Good. It's about time that refs tested epees using the equivalent mass of the energy of a photon given its frequency, via the Planck constant.

Yes, I'm afraid every armorer in the world is now going to have to build their own Watt balance: Out of Lego, of course.

Funny. The new definition of a kilogram was done in such a way that a newly defined kg matches exactly the old definition of a kilogram at the time when the new standard goes in effect. There is no change for any practical purposes.