Rizzo is now tied for 9th in the majors in steals. He's only 2 off Jacoby Ellsbury and only 6 back of Hamilton. I don't want to get over dramatic about a 100 PA sample here but if you project his numbers over say 700 PAs you're talking about 26 HRs, 46 SB and a .313/.458/.530 to go along with some where between an 8-14 UZR/150(basically what he's been the past 3 years). I don't think there's any way in hell he steals 46 bases but if he gets say 20 those are near Mike Trout numbers. Trout's best fWAR season was 2013 where he had 716 PAs, 27 HRs, 33 SB, .323/.432/.557 with a 4.0 UZR/150 across all the OF positions. That was a 10.5 fWAR season.
He's got a very real shot at putting up the best fWAR season in cubs history. Top 5 right now are 2001 Sosa(9.9), 1959 Banks(9.7), 1967 Santo(9.5), 1958 Banks(8.7), and 1964 Santo(8.7). Other than Sosa, none of the other 4 have a wRC+ above 164. Rizzo currently sits at 175. Sosa was 186 but Rizzo's defense is helping him out some more than Sosa's.
The great part is i'm not seeing any clearly obvious areas that are flukey. His BABIP is elevated at .333 but it's not crazy and given he's walking more than striking out(14.0%/13.1%) and with such a high contact rate that doesn't seem that unusual. His BABIP last year was .311 and clearly he's playing better so not that surprising to see a slight bump. His power has actually been down from last year .217 ISO compared to .240. So, that's an area he could conceivably be better. The SBs might come down but they aren't *that* big a part of his value and getting 13 over 138 games when you have 7 over 26 doesn't seem crazy. Last season he had 6 over 140 and is clearly running more.
All I can say is this is going to be a fun season to watch statistically.