Bubbles exist when too much money chases too little returns driving up valuations of an asset. Bursting occurs when sufficient investors see that the emperor is naked and run for the exit simultaneously. The potential for this seems high given  the astronomical amount of funding being poured into startups.  Hundreds of billions of dollars every year.  Most of it wasted and yet a seemingly unending supply.  
The fact is that most of this is venture capital and so accepting of higher risk. Profit is the reward for taking risk. So once again we have the balance between fear of missing out and fear of losing.  
The fact is that the smart money makes money.  The dumb money is blown.  Just like the long tail in content or pharmaceuticals the blockbusters in startups keep the roller coaster running. 
So as long as there are a number of high multiple exits and IPO’s or rapidly rising funding rounds there will be an inflating of the bubble. 
There can’t be a bursting of this bubble though.  Mainly because this is a very illiquid market.  So everyone can’t rush for the exit at the same time. There just won’t be any incoming funding meaning a number of start ups “finish down”! Extensive bankruptcies across the ecosystem. 
So no bursting bubble.   Just a quiet deflation back to normality. Remember the dotcom bubble? The real headline news was the blowout in listed share prices for these overvalued cash burning giants.  That could still be coming.