It's been done before (wasn't the year of Tom Simpson's death the very last occassion?) and, I suppose, it could end up a bit like the world champs where riders (usually Italians) chase down their own countryman due to trade team interests.
And what about the Giro and the Vuelta? At the moment, whilst the TdF is the biggest bike race in the world (except for the West Wales 10) the three GT's are still 'equal'. Doing this would seem to set the TdF apart and put the Giro and Vuelta's organisers noses out of joint.
My opinion - Keep it as it is but definitely apply your 3 year team ban and individual lifetime ban.
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"The most important thing in life is not to have the most, but to need the least.” Plato (my favourite Disney character).