No, but maybe we can guess?

Uber had 170 employees in Jan 2013 and were valued at $3.5 billion in Aug 2013. Their goal was to 4x the number of employees by end of 2013. They then had 1500 employees in Oct 2014 at a valuation of around $17 billion.

Let's say equity grants ranged in value from $50,000 to $200,000 (these are probably good 25th and 75th percentiles) in stock options.

The secondary is at $48 billion, which is an increase of 14x over the 2013 valuation and 3x over the 2014 valuation. Assume Uber had 600 employees at the time of the $3.5bn valuation.

The 2013 equity grants are now worth $700,000 to $2,800,000 (conservatively).

So I'd say 600-700 millionaires from that alone. Probably a whole bunch more if you count later larger grants times the smaller multiples.

So maybe 1000 millionaires?

Also, employees are only able to sell 50% of vested I believe in this round and will have to pay tax up to 40%. So that reduces the number a bit.

40%?

Is that tax amount typical?

If you're doing short term cap gains then you have to report as regular income. If you have over $526,443 in taxable income in California then your total income tax rate is actually 51.9% (39.6% federal, 12.3% state).

Is there additional time pressure based on the possible tax reform being pushed through Congress? As in does this deal become much worse/better for employees with the new code?

Hard to tell. The new tax plan is supposed to get rid of AMT which could be good for exercising options, but it also might get rid of the SALT deduction which would be pretty bad for CA taxpayers. Hard to say for sure.

No. Also individuals would have to opt into this, so it's entirely variable.