Tough to predict, because a decade is a long time - there will be young batsmen who would start to deliver by the middle of the decade (second half) while some established players will fade away by the first half of the decade. I don't think any player U23 can reach there because he'll not have enough time while players over 29 might not have a full decade to dominate. In that regard, players like Smith, Williamson, Butler, Kohli are a bit unlucky as their peak years crossing in between two decades. I think, I'll stick to the players between the age of 23-29, because most of them will get full decade.
Test Batsman of the Decade: Marnus Labuschagne - he is 26 (& Australian 26), averaging 63+ and he'll play the full decade, that means another 130+ Tests: a career of 150+ Tests, 12,000+ runs at 55+ average, 35+ hundreds and lots, lots of Test wins under his belt. The way Test cricket is moving and direct W/L are happening, won't be surprised if Marnus ends up with highest amount of Test runs in a win.
ODI batsman of the Decade: This one is a bit tricky - Babar is at his prime and he'll play full decade, De Kock is almost 28, likely to stop keeping and play full decade as well and there is my surprise pick - I am surprised no one picked this kid, Nicklus Pooran and Root also is just 29 now and that's English 29 - won't be surprised if he plays till 2031 WC - he is massively under-rated as well. I'll go with De Kock as ODI batsman of the decade.
T20 Batsman of the Decade: Probably Babar, KL has a good chance as well and that WIN kid Hetmyer can be the next Gayle if he can sort his game, still only 23 now.
The problem with Babar is that PAK doesn't play enough Test, neither those Gala 4-5 Tests series where he can pile-up 5-600 runs dominating the series - individually as well, he is officially 26 and still doesn't have a Test 150, still averaging under 45 - no chance in Test cricket. In ODI as well, PAK plays too many soft ODIs and not likely to dominate the game in next decade - Babar can pile-up stats, but may not be the reputation of a feared batsman. In T20 Babar has the best chance because PAK/PCB puts highest importance on T20s, plays too many soft T20s and plays too many good players in soft games - he'll play against Nepal reserves as well. To me, only T20s that matters is ICC events and PAK has the best chance to do well in T20s among three formats, hence Babar has a very good chance to end up as the best t20 batsman of the decade.
Test Bowler of the Decade: KG Rabada - Cummins is the closest threat but not likely to play whole decade
ODI bowler of the decade: Jofra Archer - this one is a tight call, but I went for the younger one, who plays for the best ODI team and likely to dominate ODI cricket world for years to come.
T20 bowler of the decade: Rashid Khan. Among pacers Shaheen has a very high celling as well
For Test bowling, again Rabda & Archer has the best chance to play many games and play for full decade. I would put two other names here as well - Bumrah & Cummins, but not sure if Bumrah can last even half the decade while Cummins won't play full decade, I can bet on that, Aussies don't linger their career because they know if they try, they'll be dumped unceremoniously - hence Rabada stands out. For ODI, I have already explained why Archer. Spin is the king of T20s and this guy Rashid is damn good in T20s, his team is also better in T20 than other formats. Also, being spinner, even if I take about 10-12 years discount on his official age of 21, he is likely to play entire decade and he'll play every game for AFGs. I think, it'll be contested well between Rashid, Archer & Shaheen for the T20 bowling title. From PAK's perspective, Shaheen can be a very good all-round bowler, but he'll be handicapped by the quality of his partners and his team as well - probably will end-up as a better t20 player than Test & ODI, just like Babar.
Best player of the decade: Tough, tough call - I probably will go in between Rabada or Archer. Both will dominate the longer two formats of the game, and Rabada might be the Captain as well.
Best all-rounder: This one is the trickiest one - Stokes is 29, therefore almost certainly he'll play almost entire decade, but not sure if he'll remain as an all-rounder. May be a very good batsman who bowls a bit, but not as pure all-rounder - same is likely for Pandeya in LO cricket. Considering the team profile and age, probably Holder (5 months younger than Stokes) has better celling as all-rounder to last for the decade. Two young cricketers has very good future as all-rounder - Shadab in LO cricket - he'll play lots of T20s and ODI but might not that many Tests. At official 23, Miraz has 89 wickets & 577 runs in 20 Tests with 2 10fors and 7 5fors and he'll play many Tests at home - another 70+ Tests in decade for close to 2500 runs and 300 wickets makes a very good potential for the decade and he'll lead BD for good part of the decade as well.
Apart from this list, there are some stunning U23 players who can make their names in this decade
: Gill, Jaswal, Shaw, Pope, Janneman Malan (No one noticed this kid, but can be the best batsman of the decade!!!!), Pucovski, Wiaan Mulder, Hetmayer
My surprise team of the decade is SAF - I read lots of negatives about their demise in cricket, but some of the best young cricketers are being cooked there - Rabada, Malan, Mulder, Verryene, Sipamla, Ngidi, Markram, Hamza. The Kolpak route is going to be closed and I am sure we'll see a raise in SAF cricket in this decade.