I would love to see Santa become more longtermist. 

• Santa travels at speeds in excess of 4 million km/h (source) in order to travel 160 million km to visit 200 million children in one night. This suggests that Santa has access to very powerful energy source. Research into this could swiftly accelerate clean energy research. This could (a) quickly resolve the climate crisis and (b) leave fossil fuels in the ground which would allow for a quick recovery to civilisation in case of future civilisational collapse. Santa's failure to share this potentially humanity-saving power with everyone surely makes him very s-elf-ish.
• As someone who has lived since the third to fourth century, Santa certainly has a very valuable perspective on the long term past. I'd like to see Santa contribute as a historian to help us better understand the long term future. I'd also expect Santa to be well-positioned to collaborate with Rudolph on a longtermist history project, because many have predicted: "Rudolph the red-nosed reindeer, you'll go down in historyyyy!"

I think Santa should be more anti-speciesist. 

• His presents go overwhelmingly to human children. I'm sure many young animals feel they are missing out simply because they happen not have been born human. Where is Santa Paws?
• Santa gets his reindeer to travel at the aforementioned >4 million km/h. It seems highly unlikely that this would be consistent with how reindeer would behave in their natural environment. However, there is some reason to believe that Santa may care for his reindeer. After all, when all of the other reindeer used to laugh and call names at one particular reindeer, Santa did intervene and grant that reindeer a leadership position which effectively ended the bullying. Perhaps, therefore, Santa may love animals deerly.

Santa could do more as an impact investor too.

• Like all other philanthropists, Santa should remember that his money is being invested before it is donated. I'm sure Santa must deal with some money, probably to purchase the raw materials which his elves use in their workshop, or failing that he at least handles the chocolate coins which appear in so many stockings. Enough money to fund 200 million children's worth of presents suggests an endowment of many billions. Santa could use this to fund more impact investing evaluations, using the Total Portfolio Return framework. For any leftover funds, he could invest in a Universal Ownership approach to help transform the financial system for the better. This makes sense for Santa, or anyone else who is not nickel-less.

Santa could also do more in terms of short-termist happiness.

• Some research suggests that therapy may be 12x better than cash transfers. But how effective are gift transfers? Maybe Santa could outperform his current impact by focusing more on mental elf.

Santa could also do more charity entrepreneurship.

• What better way to be more ambitious than to set up a new charity? Perhaps Santa was suffering from misconceptions about what sort of person you need to be to found a charity. Santa is clearly a quiet man -- I've never spotted him bringing presents to my home -- and therefore perhaps quite introverted. However he should learn that to be a charity founder you don't need to be brimming in elf-confidence.

I'm not sure how relevant this is to Effective Altruism, but I found this video about what would realistically happen geopolitically if Santa actually existed.