The concept of generic fragments has come up quite a lot, and I think would be beneficial in a lot of areas in the game.  Other areas include:

• The clan shop - after you finish Yannica and/or Yakarl you should have an option to get generic fragments (it would still only be 5 per week).  
• The Tag Team Arena Bazaar - Similar to above, but once you finish Drex you should be able to buy 1 generic fragment a day or something, assuming you have the gold bars
• Token Trader - whereby instead of buying legendary champions, you could buy generic fragments.  This would make people use duplicate legendaries to complete old fragment events
• Events like the forge pass and the path of light - The rewards were pretty underwhelming in both of these events, and having things like generic fragments up for grabs would have dramatically improved interest and participation
• Shop purchases - as another source of income for Plarium, they could sell packs of generic fragments every now and then

Hell, they can even put them as rewards for coming in first or second in tournaments or something

What incentive will there be for people to spend money to complete fusions?

People who spend will spend.  People who don't spend won't spend.

I agree with the second statement. 

But spenders will spend less if they get something for free. 

The upside for plarium is 0, the downside is significant. 

Having generic fragments for sale in the shop will increase sales.  Having generic fragments in path of light and forge pass events will increase sales, especially if it's in the paid line of the latter.  More people would participate if it means gaining something to help contribute to old events

By the way, I wasn't proposing that every suggestion above is implemented, because I think that would make it so that there are too many generic fragment sources in the game.  I meant that there are other areas where a generic fragment reward could be included in addition to Hydra rewards.  It could still be limited to a single area.

The concept of generic fragments has come up quite a lot, and I think would be beneficial in a lot of areas in the game.  Other areas include:

• The clan shop - after you finish Yannica and/or Yakarl you should have an option to get generic fragments (it would still only be 5 per week).  
• The Tag Team Arena Bazaar - Similar to above, but once you finish Drex you should be able to buy 1 generic fragment a day or something, assuming you have the gold bars
• Token Trader - whereby instead of buying legendary champions, you could buy generic fragments.  This would make people use duplicate legendaries to complete old fragment events
• Events like the forge pass and the path of light - The rewards were pretty underwhelming in both of these events, and having things like generic fragments up for grabs would have dramatically improved interest and participation
• Shop purchases - as another source of income for Plarium, they could sell packs of generic fragments every now and then

Hell, they can even put them as rewards for coming in first or second in tournaments or something

You meant to say, that would be great but never going to happen... 😆