Could more objects from the Oort cloud with highly elliptical orbits be discovered in the future?

Question

It took the modern astronomy to live to the year of 2014 to discover 2014 UN271¹ (sized roughly 100-200 km and now being re-qualified from a comet to mini object), which has "extremely" elliptical orbit with the ~600,000 years period and the next nearest to Earth position to be in 2031. Note that in this case the lead time between the object discovery and it's reaching the closest to Earth position is 17 years... So perhaps eventually other objects with such elliptical orbits and periods exceeding the historical age of the observational astronomy which itself is not to exceed 10,000 years, counting from human naked eye intelligent ability to observe celestial bodies could be discovered in the future? How large in size those objects could be, how close to Earth those objects could pass, what are the probabilities of such objects to hit the Earth and what could be the range of the lead times for such objects between their discoveries and them reaching the closest to Earth position? Could it be assumed that there is a probability of existence of undiscovered yet Oort objects with elliptical orbits and with size/weight parameters being equal or greater than such of Mercury (4,879 km across and 330 trillion tons correspondingly)?

PS https://phys.org/visualstories/2021-03-interstellar-solar-year.amp

The team of scientists lead by Marshall Eubanks of Interstellar Exploration Initiative organization published the study in Naked Science magazine in March 2021, which estimates that about 7 interstellar objects pass through the inner solar system every year.

¹From Earthsky.org's Mega Comet Inbound From Oort Cloud

The newly discovered mega comet, 2014 UN271, is currently diving from the outer solar system. At its closest to our sun, it’ll come close to the orbit of the outer planet Saturn in 2031

Answer 1

If you consider "objects" to include comets, then yes, they will be, probably within a few months.

Extremely long-period comets are continually being discovered by various space telescopes and surveys like NEOWISE, Pan-STARRS, and ATLAS. Looking at Wikipedia's List of near-parabolic comets, 6 of the 32 near-parabolic comets listed as being discovered in 2020 have computed periods of over 10,000 years.

Answer 2

Although, there hasn't been a confirmed direct observations of the Oort cloud, it is confirmed to be the home of long period comets. Some notable examples include C/1999 F1 (Catalina), C/2006 P1 (McNaught), C/2010 X1 (Elenin), Comet ISON, C/2013 A1 (Siding Spring), C/2017 K2, and C/2017 T2 (PANSTARRS).

Oort-originated comets finds difficulty entering the inner Solar system. Hence observations on them have been quite difficult. From Wikipedia:

Oort noted that the number of returning comets was far less than his model predicted, and this issue, known as "cometary fading", has yet to be resolved. No dynamical process are known to explain the smaller number of observed comets than Oort estimated. Hypotheses for this discrepancy include the destruction of comets due to tidal stresses, impact or heating; the loss of all volatiles, rendering some comets invisible, or the formation of a non-volatile crust on the surface. Dynamical studies of hypothetical Oort cloud comets have estimated that their occurrence in the outer-planet region would be several times higher than in the inner-planet region. This discrepancy may be due to the gravitational attraction of Jupiter, which acts as a kind of barrier, trapping incoming comets and causing them to collide with it, just as it did with Comet Shoemaker–Levy 9 in 1994. An example of a typical dynamically old comet with an origin in the Oort cloud could be C/2018 F4.

Nevertheless, comets which do enter the inner Solar system are detected and characterized and more such comets would likely to get detected in the near future (with improved technology and instruments).

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Update(addressing interstellar objects)

Although astronomers estimates several interstellar object passing through the solar system, only two interstellar objects has been confirmed and characterized as of now (ʻOumuamua and 2I/Borisov). Interstellar objects are very difficult to detect and charcterize due to numerous reasons, all of which is mentioned in this paper (Hajdukova et.al 2020):

Owing to the difficulties in obtaining accurate meteor measurements and, consequently, the meteoroids’ orbital parameters, the identification of interstellar meteors based on their hyperbolic excess velocities is extremely challenging. Moreover, it has to be verified whether the orbit’s hyperbolicity was not produced in the Solar System. Searches for interstellar meteors have been carried out using different observational techniques for more than a quarter of a century and, although they have produced many valuable results, not a single case of a meteor claimed to be produced by an interstellar particle has proven satisfactorily convincing.