Does tidyverse offer xts range-based queries?

No dplyr or tidyverse does not have such syntax. You may use filter like

library(dplyr)

willsh %>% 
   filter(Date >= as.Date("1979-12-31"), Date <= as.Date("2017-12-31"))

Or use between :

willsh %>%
  filter(between(Date, as.Date("1979-12-31"), as.Date("2017-12-31")))

lubridate has interval class. Any of these can be used to represent the interval from 1979-12-31 to 2017-12-31.

library(dplyr)
library(lubridate)

ival1 <- interval("19791231/20171231")
ival1a <- interval("1979-12-31/2017-12-31") 
ival2 <- interval("19791231/P38Y")
ival2a <- interval("1979-12-31/P38Y")
ival3 <- interval(ymd(19791231), ymd(20171231))
ival3a <- interval(ymd("1979-12-31"), ymd("2017-12-31"))

sapply(list(ival1, ival1a, ival2, ival2a, ival3, ival3a), identical, ival1)
## [1] TRUE TRUE TRUE TRUE TRUE TRUE

%within% can be used to check whether a date falls in an interval.

ymd(c(19791230, 19791231, 19800101, 20171230, 20171231, 20180101)) %within% ival1
## [1] FALSE  TRUE  TRUE  TRUE  TRUE FALSE

We can use it like this:

# test input
willsh <- tibble(Date = seq(ymd(19700101), ymd(20210101), by = "10 year"), 
             year = year(Date))

willsh %>% filter(Date %within% interval("1979-12-31/2017-12-31"))
## # A tibble: 4 x 2
##   Date        year
##   <date>     <dbl>
## 1 1980-01-01  1980
## 2 1990-01-01  1990
## 3 2000-01-01  2000
## 4 2010-01-01  2010

We can use

library(data.table)
setDT(willsh)[between(Date, as.IDate("1979-12-31"), as.IDate("2017-12-31"))]